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The National Institute of Astrophysics, Optics and Electronics is a Mexican science research institute located in Tonantzintla, Puebla. Founded by presidential decree on 11 November 1971, it has over 100 researchers in astrophysics, optics, electronics and computing science, with postgraduate programs in these areas. INAOE is one of 30 public research centers sponsored by the National Council of Science and Technology of Mexico . The Institute, in partnership with the University of Massachusetts Amherst, developed the Large Millimeter Telescope / Gran Telescopio Milimétrico on the Puebla-Veracruz border. Wikipedia.

Lucchesi D.M.,National institute for astrophysics | Lucchesi D.M.,CNR Institute of Information Science and Technologies Alessandro Faedo
Advances in Space Research | Year: 2011

LAGEOS II general relativity pericenter precession has been analysed in terms of the errors produced by the mismodelling of both the gravitational and non-gravitational perturbations acting on the satellite orbit. The accuracy in the pericenter determination may be considered as an upper-bound value for the estimate of the strength α of a possible new-long-range-interaction described by a Yukawa-like potential. In the present work we have focused on the constraints in α that can be obtained with the current best multi-satellites gravity field model EGM96 (α < 2.6 × 10 -10) and also with the first promising models from the CHAMP (α < 1.8 × 10-10) and GRACE (α < 1.2 × 10 -10) gravimetric missions. These results represent, potentially, an improvement of two or three orders-of-magnitude with respect to the best constraints obtained in the past with Earth-LAGEOS and Lunar-LAGEOS data (|α| < 10-5-10-8). The impact of the non-gravitational perturbations mismodelling in the final error budget has been determined together with the improvements obtainable in the constraint of the strength α with the proposed LARES satellite. © 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.

Pariani G.,Polytechnic of Milan | Bertarelli C.,Polytechnic of Milan | Dassa G.,Polytechnic of Milan | Bianco A.,National institute for astrophysics | Zerbi G.,Polytechnic of Milan
Optics Express | Year: 2011

The development of photochromic Computer Generated Holograms (CGHs) to test any complex optics, such as aspheres and free-form optics, is described. A thermally irreversible photochromic polyurethane has been synthesized to give good thin films with a strong modulation of the optical transmission. The photochromic CGH has been tested with a simple interferometrical configuration showing promising results. The use of photochromic CGHs provides advantages over standard technologies, as rewritability and self developing. © 2011 Optical Society of America.

Sulentic J.W.,Institute Astrofisica Of Andalucia | Marziani P.,National institute for astrophysics | Zamfir S.,University of Wisconsin - Stevens Point | Meadows Z.A.,University of Wisconsin - Stevens Point
Astrophysical Journal Letters | Year: 2012

We test the recent claim by Hu et al. that Fe II emission in type 1 active galactic nuclei shows a systematic redshift relative to the local source rest frame and broad-line Hβ. We compile high signal-to-noise median composites using Sloan Digital Sky Survey spectra from both the Hu et al. sample and our own sample of the 469 brightest DR5 spectra. Our composites are generated in bins of FWHM Hβ and Fe II strength as defined in our 4D Eigenvector 1 formalism. We find no evidence for a systematic Fe II redshift and consistency with previous assumptions that Fe II shift and width (FWHM) follow Hβ shift and FWHM in virtually all sources. This result is consistent with the hypothesis that Fe II emission (quasi-ubiquitous in type 1 sources) arises from a broad-line region with geometry and kinematics the same as that producing the Balmer lines. © 2012. The American Astronomical Society. All rights reserved.

Testa P.,Smithsonian Astrophysical Observatory | Reale F.,University of Palermo | Reale F.,National institute for astrophysics
Astrophysical Journal Letters | Year: 2012

We use coronal imaging observations with the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), and Hinode/Extreme-ultraviolet Imaging Spectrometer (EIS) spectral data to explore the potential of narrowband EUV imaging data for diagnosing the presence of hot (T ≳ 5MK) coronal plasma in active regions. We analyze observations of two active regions (AR 11281, AR 11289) with simultaneous AIA imaging and EIS spectral data, including the Ca XVII line (at 192.8Å), which is one of the few lines in the EIS spectral bands sensitive to hot coronal plasma even outside flares. After careful co-alignment of the imaging and spectral data, we compare the morphology in a three-color image combining the 171, 335, and 94Å AIA spectral bands, with the image obtained for Ca XVII emission from the analysis of EIS spectra. We find that in the selected active regions the Ca XVII emission is strong only in very limited areas, showing striking similarities with the features bright in the 94Å (and 335Å) AIA channels and weak in the 171Å band. We conclude that AIA imaging observations of the solar corona can be used to track hot plasma (6-8MK), and so to study its spatial variability and temporal evolution at high spatial and temporal resolution. © 2012. The American Astronomical Society. All rights reserved.

Bemporad A.,National institute for astrophysics
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2011

Since the launch of the STEREO mission (October 2006) the determination of the real prominence shapes and trajectories during eruptions in three dimensions (3D) became easily viable, thanks to the stereoscopic observations, available for the first time, acquired by the twin STEREO spacecraft. These data give us now a unique capability to identify twisted or ribbon-like structures, helical or planar motions, and to investigate the existence of a real critical height for prominence eruptions without projection effects. All these parameters are of fundamental importance for understanding the physical phenomena triggering the eruption and affecting their early evolution. Many different techniques have been developed and employed after the beginning of the "STEREO era", but important information on the 3D structure of prominences was also derived before STEREO. Hence, the present paper is aimed at reviewing different reconstruction techniques developed both before and after the availability of stereoscopic observations and discusses the advancement made so far on these issues thanks to the pre- and post-STEREO data. © 2010 Elsevier Ltd.

Maoz D.,Tel Aviv University | Mannucci F.,National institute for astrophysics | Nelemans G.,Radboud University Nijmegen | Nelemans G.,Catholic University of Leuven
Annual Review of Astronomy and Astrophysics | Year: 2014

Type Ia supernovae (SNe Ia) are important distance indicators, element factories, cosmic-ray accelerators, kinetic-energy sources in galaxy evolution, and end points of stellar binary evolution. It has long been clear that a SN Ia must be the runaway thermonuclear explosion of a degenerate carbon-oxygen stellar core, most likely a white dwarf (WD). However, the specific progenitor systems of SNe Ia, and the processes that lead to their ignition, have not been identified. Two broad classes of progenitor binary systems have long been considered: single-degenerate (SD), in which a WD gains mass from a nondegenerate star; and double-degenerate (DD), involving the merger of two WDs. New theoretical work has enriched these possibilities with some interesting updates and variants. We review the significant recent observational progress in addressing the progenitor problem. We consider clues that have emerged from the observed properties of the various proposed progenitor populations, from studies of SN Ia sites pre- and postexplosion from analysis of the explosions themselves and from the measurement of event rates. The recent nearby and well-studied event, SN 2011fe, has been particularly revealing. The observational results are not yet conclusive and sometimes prone to competing theoretical interpretations. Nevertheless, it appears that DD progenitors, long considered the underdog option, could be behind some, if not all, SNe Ia. We point to some directions that may lead to future progress. Copyright © 2014 by Annual Reviews.

Zhu X.-J.,Beijing Normal University | Fan X.-L.,University of Trieste | Fan X.-L.,National institute for astrophysics | Zhu Z.-H.,Beijing Normal University
Astrophysical Journal | Year: 2011

We revisit the possibility and detectability of a stochastic gravitational wave (GW) background produced by a cosmological population of newborn neutron stars (NSs) with r-mode instabilities. The NS formation rate is derived from both observational and simulated cosmic star formation rates (CSFRs). We show that the resultant GW background is insensitive to the choice of CSFR models, but depends strongly on the evolving behavior of CSFR at low redshifts. Nonlinear effects such as differential rotation, suggested to be an unavoidable feature which greatly influences the saturation amplitude of the r-mode, are considered to account for GW emission from individual sources. Our results show that the dimensionless energy density ΩGW could have a peak amplitude of ≃(1-3.5) × 10-8 in the frequency range (200-1000) Hz, if the smallest amount of differential rotation corresponding to a saturation amplitude of order unity is assumed. However, such a high-mode amplitude is unrealistic as it is known that the maximum value is much smaller and at most 10-2. A realistic estimate of ΩGW should be at least four orders of magnitude lower (∼10-12), which leads to a pessimistic outlook for the detection of the r-mode background. We consider different pairs of terrestrial interferometers (IFOs) and compare two approaches to combine multiple IFOs in order to evaluate the detectability of this GW background. Constraints on the total emitted GW energy associated with this mechanism to produce a detectable stochastic background (a signal-to-noise ratio of 2.56 with 3 year cross-correlation) are ∼10-3 M⊙ 1 c 2 for two co-located advanced LIGO detectors, and 2 × 10-5 M⊙ 1 c 2 for two Einstein telescopes. These constraints may also be applicable to alternative GW emission mechanisms related to oscillations or instabilities in NSs depending on the frequency band where most GWs are emitted. © 2011. The American Astronomical Society. All rights reserved.

Swaters R.A.,University of Maryland University College | Sancisi R.,National institute for astrophysics | Sancisi R.,University of Groningen | Van Albada T.S.,University of Groningen | Van Der Hulst J.M.,University of Groningen
Astrophysical Journal | Year: 2011

Mass models for a sample of 18 late-type dwarf and low surface brightness galaxies show that in almost all cases the contribution of the stellar disks to the rotation curves can be scaled to explain most of the observed rotation curves out to two or three disk scale lengths. The concept of a maximum disk, therefore, appears to work as well for these late-type dwarf galaxies as it does for spiral galaxies. Some of the mass-to-light ratios required in our maximum disk fits, however, are high, up to about 15 in the R band, with the highest values occurring in galaxies with the lowest surface brightnesses. Equally well-fitting mass models can be obtained with much lower mass-to-light ratios. Regardless of the actual contribution of the stellar disk, the fact that the maximum disk can explain the inner parts of the observed rotation curves highlights the similarity in shapes of the rotation curve of the stellar disk and the observed rotation curve. This similarity implies that the distribution of the total mass density is closely coupled to that of the luminous mass density in the inner parts of late-type dwarf galaxies. © 2011. The American Astronomical Society. All rights reserved.

Tombesi F.,NASA | Tombesi F.,University of Maryland University College | Cappi M.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Reeves J.N.,Keele University | And 2 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

Using the results of a previous X-ray photoionizationmodelling of blueshifted Fe K absorption lines on a sample of 42 local radio-quiet AGNs observed with XMM-Newton, in this Letter we estimate the location and energetics of the associated ultrafast outflows (UFOs). Due to significant uncertainties, we are essentially able to place only lower/upper limits. On average, their location is in the interval ~0.0003-0.03 pc (~10 2-10 4r s) from the central black hole, consistent with what is expected for accretion disc winds/outflows. The mass outflow rates are constrained between ~0.01 and 1M ⊙ yr -1, corresponding to ≳ 5-10 per cent of the accretion rates. The average lower/upper limits on the mechanical power are log Ė K ≃42.6-44.6 erg s -1. However, the minimum possible value of the ratio between the mechanical power and bolometric luminosity is constrained to be comparable or higher than the minimum required by simulations of feedback induced by winds/outflows. Therefore, this work demonstrates that UFOs are indeed capable to provide a significant contribution to the AGN cosmological feedback, in agreement with theoretical expectations and the recent observation of interactions between AGN outflows and the interstellar medium in several Seyfert galaxies. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Bird S.,Institute of Astronomy and Kavli Institute for Cosmology | Viel M.,National institute for astrophysics | Viel M.,National Institute of Nuclear Physics, Italy | Haehnelt M.G.,Institute of Astronomy and Kavli Institute for Cosmology
Monthly Notices of the Royal Astronomical Society | Year: 2012

We perform an extensive suite of N-body simulations of the matter power spectrum, incorporating massive neutrinos in the range M ν= 0.15-0.6eV, probing the non-linear regime at scales k < 10hMpc -1 at z < 3. We extend the widely used halofit approximation to account for the effect of massive neutrinos on the power spectrum. In the strongly non-linear regime, halofit systematically overpredicts the suppression due to the free streaming of the neutrinos. The maximal discrepancy occurs at k∼ 1hMpc -1, and is at the level of 10 per cent of the total suppression. Most published constraints on neutrino masses based on halofit are not affected, as they rely on data probing the matter power spectrum in the linear or mildly non-linear regime. However, predictions for future galaxy, Lyman α forest and weak lensing surveys extending to more non-linear scales will benefit from the improved approximation to the non-linear matter power spectrum we provide. Our approximation reproduces the induced neutrino suppression over the targeted scales and redshifts significantly better. We test its robustness with regard to changing cosmological parameters and a variety of modelling effects. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Santini P.,National institute for astrophysics
Journal of Physics: Conference Series | Year: 2011

In recent years, several surveys have shown that massive galaxies have undergone a major evolution during the epoch corresponding to the redshift range 1.5-3, assembling a significant fraction of their stellar mass at that epoch. To understand the origin of this rapid rise, a closer scrutiny on the nature and physical properties of massive galaxies at high redshift is needed. I will present our recent results based on the analysis of the 24 μm MIPS data of the GOODS-S field, that allow to trace star formation (or the lack of it) in high redshift galaxies without biases due to dust extinction. I will show the results of our analysis focusing in particular on the fraction of quiescent galaxies as a function of redshift and the evolution of the specific star formation rate as a function of redshift and stellar mass. The scenario emerging from these data will be compared with recent predictions of theoretical models to discuss the validity of their physical ingredients. The main results of this work are: a) the fraction of quiescent galaxies decreases with redshift, and a non-negligible fraction (∼15%) is already in place at z ∼ 3; b) massive star-forming galaxies are vigorously forming stars (∼ 300M ⊙yr -8) at z ∼ 2, and during this epoch they assemble a substantial part of their final stellar mass; c) the specific star formation rate shows a bimodal distribution up to z ∼ 2; d) theoretical predictions, although qualitatevely in agreement, are unable to quantitatively reproduce these observations. © Published under licence by IOP Publishing Ltd.

Lyutikov M.,Purdue University | Lyutikov M.,National institute for astrophysics | Lyutikov M.,University of Toronto | Lazarian A.,University of Wisconsin - Madison
Space Science Reviews | Year: 2013

Astrophysical plasmas can have parameters vastly different from the more studied laboratory and space plasmas. In particular, the magnetic fields can be the dominant component of the plasma, with energy-density exceeding the particle rest-mass energy density. Magnetic fields then determine the plasma dynamical evolution, energy dissipation and acceleration of non-thermal particles. Recent data coming from astrophysical high energy missions, like magnetar bursts and Crab nebula flares, point to the importance of magnetic reconnection in these objects. In this review we outline a broad spectrum of problems related to the astrophysical relevant processes in magnetically dominated relativistic plasmas. We discuss the problems of large scale dynamics of relativistic plasmas, relativistic reconnection and particle acceleration at reconnecting layers, turbulent cascade in force-fee plasmas. A number of astrophysical applications are also discussed. © 2013 Springer Science+Business Media Dordrecht.

Brunetti G.,National institute for astrophysics | Jones T.W.,University of Minnesota
International Journal of Modern Physics D | Year: 2014

Radio observations prove the existence of relativistic particles and magnetic field associated with the intra-cluster-medium (ICM) through the presence of extended synchrotron emission in the form of radio halos and peripheral relics. This observational evidence has fundamental implications on the physics of the ICM. Nonthermal components in galaxy clusters are indeed unique probes of very energetic processes operating within clusters that drain gravitational and electromagnetic energy into cosmic rays (CRs) and magnetic fields. These components strongly affect the (micro-)physical properties of the ICM, including viscosity and electrical conductivities, and have also potential consequences on the evolution of clusters themselves. The nature and properties of CRs in galaxy clusters, including the origin of the observed radio emission on cluster-scales, have triggered an active theoretical debate in the last decade. Only recently we can start addressing some of the most important questions in this field, thanks to recent observational advances, both in the radio and at high energies. The properties of CRs and of cluster nonthermal emissions depend on the dynamical state of the ICM, the efficiency of particle acceleration mechanisms in the ICM and on the dynamics of these CRs. In this paper, we discuss in some detail the acceleration and transport of CRs in galaxy clusters and the most relevant observational milestones that have provided important steps on our understanding of this physics. Finally, looking forward to the possibilities from new generations of observational tools, we focus on what appear to be the most important prospects for the near future from radio and high-energy observations. © World Scientific Publishing Company.

Papai P.,University of Hawaii at Manoa | Szapudi I.,University of Hawaii at Manoa | Granett B.R.,National institute for astrophysics
Astrophysical Journal | Year: 2011

We build a model for the density and integrated Sachs-Wolfe (ISW) profile of supervoid and supercluster structures. Our model assumes that fluctuations evolve linearly from an initial Gaussian random field. We find these assumptions capable of describing N-body simulations and simulated ISW maps remarkably well on large scales. We construct an ISW map based on locations of superstructures identified previously in the Sloan Digital Sky Survey Luminous Red Galaxy sample. A matched filter analysis of the cosmic microwave background confirms a signal at the 3.2σ confidence level and estimates the radius of the underlying structures to be 55 ± 28 h -1 Mpc. The amplitude of the signal, however, is 2σ higher than ΛCDM predictions. © 2011. The American Astronomical Society. All rights reserved.

Southworth J.,Keele University | Bruni I.,National institute for astrophysics | Mancini L.,Max Planck Institute for Astronomy | Gregorio J.,Grupo Atalaia
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present photometry of four transits of the planetary system HAT-P-13, obtained using defocused telescopes. We analyse these, plus nine data sets from the literature, in order to determine the physical properties of the system. The mass and radius of the star are M A= 1.320 ± 0.048 ± 0.039M ⊙ and R A= 1.756 ± 0.043 ± 0.017R ⊙ (statistical and systematic error bars). We find the equivalent quantities for the transiting planet to be M b= 0.906 ± 0.024 ± 0.018M Jup and R b= 1.487 ± 0.038 ± 0.015R Jup, with an equilibrium temperature of K. Compared to previous results, which were based on much sparser photometric data, we find the star to be more massive and evolved, and the planet to be larger, hotter and more rarefied. The properties of the planet are not matched by standard models of irradiated gas giants. Its large radius anomaly is in line with the observation that the hottest planets are the most inflated, but at odds with the suggestion of inverse proportionality to the [Fe/H] of the parent star. We assemble all available times of transit mid-point and determine a new linear ephemeris. Previous findings of transit timing variations in the HAT-P-13 system are shown to disagree with these measurements, and can be attributed to small-number statistics. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Rozelot J.-P.,French National Center for Scientific Research | Damiani C.,National institute for astrophysics
European Physical Journal H | Year: 2011

The story of the solar oblateness begins in the pre-relativity days when an explanation of the observed advance of Mercury's perihelion was searched for. Then, examination of historical records during the first decade of the twentieth century shows clearly a strong effort to measure the solar shape. Results show discrepancies, due on one hand, to the fact that physical statements in the solar case are still pending (for example does the solar core rotate rapidly? Is the Sun an oblique rotator? How does the magnetic field distort the outer shape?) and on the other hand, due to the difficulty in measuring a faint quantity, even when using the cutting edge of up-to-date techniques. We provide a new perspective on the controversy which followed measurements made in Princeton (USA) in the mid-1960s, highlighting the possibility to advocate alternative theories of gravitation. Since then, the accurate shape of the Sun has been actively debated, and so far, only satellite experiments seem to achieve the required sensitivity to measure the expected faint deviations to sphericity. In a close cooperation between experiments and theory, we point out how false ideas or inexact past measurements may contribute to the advancement of new physical concepts. © EDP Sciences, Springer-Verlag 2011.

Gasperini L.,CNR Marine Science Institute | Stanghellini C.,National institute for astrophysics | Serra R.,University of Bologna
Terra Nova | Year: 2014

Several lines of evidence indicate that Cheko, a small lake close to the epicentre of the 1908 Tunguska Event (TE), fills a crater left behind by a fragment of the Tunguska Cosmic Body that impacted the ground downrange of the main explosion. It is thought that over 80 million trees were flattened or burnt as a consequence of the TE. However, a small number of trees in the devastated area survived the explosion and recorded in their growth-ring patterns the environmental changes that followed this event. Some of those trees were found around Lake Cheko, ~10 km NW of the inferred TE epicentre. We analysed new data from the floor of Lake Cheko, including seismic-reflection profiles, side-scan sonar and video images, as well as dendrochronological evidence in tree samples collected along the shores, to test the hypothesis of a 1908 formation of the lake. © 2014 John Wiley & Sons Ltd.

Barbera F.L.,National institute for astrophysics | Ferreras I.,University College London | Vazdekis A.,Institute of Astrophysics of Canarias | Vazdekis A.,University of La Laguna
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2015

The initial mass function (IMF) of early-type galaxies (ETGs) has been found to feature systematic variations by both dynamical and spectroscopic studies. In particular, spectral line strengths, based on gravity-sensitive features, suggest an excess of low-mass stars in massive ETGs, i.e. a bottom-heavy IMF. The physical drivers of IMF variations are currently unknown. The abundance ratio of α elements, such as [Mg/Fe], has been suggested as a possible driver of the IMF changes, although dynamical constraints do not support this claim. In this letter, we take advantage of the large Sloan Digital Sky Survey data base. Our sample comprises 24 781 high-quality spectra, covering a large range in velocity dispersion (100 < σ0 < 320 km s-1) and abundance ratio (-0.1 < [Mg/Fe] < +0.4). The large volume of data allows us to stack the spectra at fixed values of σ0 and [Mg/Fe]. Our analysis - based on gravity-sensitive line strengths - gives a strong correlation with central velocity dispersion and a negligible variationwith [Mg/Fe] at fixed σ0. This result is robust against individual elemental abundance variations, and seems not to raise any apparent inconsistency with the alternativemethod based on galaxy dynamics. © 2015 The Authors.

Roncadelli M.,National Institute of Nuclear Physics, Italy | Tavecchio F.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2015

Preliminary evidence of solar axions in XMM-Newton observations has quite recently been claimed by Fraser et al. as an interpretation of their detection of a seasonally-modulated excess of the X-ray background. Within such an interpretation, these authors also estimate the axion mass to be ma {minus tilde}{combining long vertical line 2.3 × 10-6 eV. Since an axion with this mass behaves as a cold dark matter particle, according to the proposed interpretation the considered detection directly concerns cold dark matter as well. So, the suggested interpretation would lead to a revolutionary discovery if confirmed. Unfortunately, we have identified three distinct problems in this interpretation of the observed result of Fraser et al. which ultimately imply that the detected signal - while extremely interesting in itself - cannot have any relation with hypothetical axions produced by the Sun. Thus, a physically consistent interpretation of the observed seasonally-modulated X-ray excess still remains an exciting challenge. © 2015 The Authors.

Buenzli E.,Max Planck Institute for Astronomy | Saumon D.,Los Alamos National Laboratory | Marley M.S.,NASA | Apai D.,University of Arizona | And 4 more authors.
Astrophysical Journal | Year: 2015

The binary brown dwarf WISE J104915.57-531906.1 (also Luhman 16AB), composed of a late-L and early-T dwarf, is a prototypical L/T transition flux reversal binary located at a distance of only 2 pc. Luhman 16B is a known variable whose light curves evolve rapidly. We present a spatially resolved spectroscopic time-series of Luhman 16A and B covering 6.5 hr using the Hubble Space Telescope/WFC3 at 1.1-1.66 μm. The small, count-dependent variability of Luhman 16A at the beginning of the observations likely stems from instrumental systematics; Luhman 16A appears non-variable above ≈0.4%. Its spectrum is well fit by a single cloud layer with intermediate cloud thickness (f sed = 2, T eff = 1200 K). Luhman 16B varies at all wavelengths with peak-to-valley amplitudes of 7%-11%. The amplitude and light curve shape changes over only one rotation period. The lowest relative amplitude is found in the deep water absorption band at 1.4 μm, otherwise it mostly decreases gradually from the blue to the red edge of the spectrum. This is very similar to the other two known highly variable early-T dwarfs. A two-component cloud model accounts for most of the variability, although small deviations are seen in the water absorption band. We fit the mean spectrum and relative amplitudes with a linear combination of two models of a warm, thinner cloud (T eff = 1300 K, f sed = 3) and a cooler, thicker cloud (T eff = 1000-1100 K, f sed = 1), assuming out-of-equilibrium atmospheric chemistry. A model with parameters as for Luhman 16A except for the addition of cloud holes cannot reproduce the variability of Luhman 16B, indicating more complex cloud evolution through the L/T transition. The projected separation of the binary has decreased by ≈0.″3 in eight months. © 2015. The American Astronomical Society. All rights reserved.

Giordano S.,National institute for astrophysics | Raymond J.C.,Harvard - Smithsonian Center for Astrophysics | Lamy P.,Laboratoire Dastrophysique Of Marseille | Uzzo M.,Computer Sciences Corp. | Dobrzycka D.,European Southern Observatory
Astrophysical Journal | Year: 2015

Comet C/2002 S2, amember of the Kreutz family of sungrazing comets,was discovered inwhite-light images of the Large Angle and Spectromeric Coronagraph Experiment coronagraph on the Solar and Heliospheric Observatory (SOHO) on 2002 September 18 and observed in H I Lyα emission by the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) instrument at four different heights as it approached the Sun. The H I Lyα line profiles detected by UVCS are analyzed to determine the spectral parameters: line intensity, width, and Doppler shift with respect to the coronal background. Two-dimensional comet images of these parameters are reconstructed at the different heights. A novel aspect of the observations of this sungrazing comet data is that, whereas the emission from most of the tail is blueshifted, that along one edge of the tail is redshifted. We attribute these shifts to a combination of solar wind speed and interaction with the magnetic field. In order to use the comet to probe the density, temperature, and speed of the corona and solar wind through which it passes, as well as to determine the outgassing rate of the comet, we develop a Monte Carlo simulation of the H I Lyα emission of a comet moving through a coronal plasma. From the outgassing rate, we estimate a nucleus diameter of about 9m. This rate steadily increases as the comet approaches the Sun, while the optical brightness decreases by more than a factor of 10 and suddenly recovers. This indicates that the optical brightness is determined by the lifetimes of the grains, sodium atoms, and molecules produced by the comet. © 2015. The American Astronomical Society. All rights reserved.

Sneden C.,University of Texas at Austin | Sneden C.,Ege University | Lucatello S.,National institute for astrophysics | Ram R.S.,University of York | And 3 more authors.
Astrophysical Journal, Supplement Series | Year: 2014

New red and violet system line lists for the CN isotopologues 13C14N and 12C15N have been generated. These new transition data are combined with those previously derived for 12C14N, and applied to the determination of CNO abundances in the solar photosphere and in four red giant stars: Arcturus, the bright, very low-metallicity star HD 122563, and the carbon-enhanced metal-poor stars HD 196944 and HD 201626. When both red and violet system lines are detectable in a star, their derived N abundances are in good agreement. The mean N abundances determined in this work are also generally in accord with published values. © 2014. The American Astronomical Society. All rights reserved..

Cellino A.,National institute for astrophysics | Bagnulo S.,College Hill | Tanga P.,University of Nice Sophia Antipolis | Novakovic B.,University of Belgrade | Delbo M.,University of Nice Sophia Antipolis
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2014

Barbarians, so named after the prototype of this class (234) Barbara, are a rare class of asteroids exhibiting anomalous polarimetric properties. Their very distinctive feature is that they show negative polarization at relatively large phase angles, where all 'normal' asteroids show positive polarization. The origin of the Barbarian phenomenon is unclear, but it seems to be correlated with the presence of anomalous abundances of spinel, a mineral usually associated with the so-called calcium-aluminium-rich inclusions (CAIs) on meteorites. Since CAIs are samples of the oldest solid matter identified in our Solar system, Barbarians are very interesting targets for investigations. Inspired by the fact that some of the few known Barbarians are members of, or very close to, the dynamical family of Watsonia, we have checked whether this family is a major repository of Barbarians, in order to obtain some hints about their possible collisional origin. We have measured the linear polarization of a sample of nine asteroids which are members of the Watsonia family within the phase-angle range 17°-21°. We found that seven of them exhibit the peculiar Barbarian polarization signature, and we conclude that the Watsonia family is a repository of Barbarian asteroids. The new Barbarians identified in our analysis will be important to confirm the possible link between the Barbarian phenomenon and the presence of spinel on the surface. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Punsly B.,ICRANet | Marziani P.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2015

Only a handful of quasars have been identified as kinetically dominated, their long-term time-averaged jet power, Q, exceeds the bolometric thermal emission, Lbol, associated with the accretion flow. This Letter presents the first extreme ultraviolet (EUV) spectrum of a kinetically dominated quasar, 3C 270.1. The EUV continuum flux density of 3C 270.1 is very steep, Fν~ν-αEUV, αEUV=2.98±0.15. This value is consistent with the correlation of Q,/Lboland αEUV found in previous studies of the EUV continuum of quasars, the EUV deficit of radio loud quasars. Curiously, although ultraviolet broad absorption line (BAL) troughs in quasar spectra are anticorrelated with Q, 3C 270.1 has been considered a BAL quasar based on an SDSS spectrum. This claim is examined in terms of the EUV spectrum of OVI and the highest resolution CIV spectrum in the archival data and the SDSS spectrum. First, from [OIII]4959,5007 (IR) observations and the UV spectral lines, it is concluded that the correct redshift for 3C 270.1 is 1.5266. It is then found that the standard measure of broad absorption, BALnicity=0, for Mg II 2800, CIV 1549 and OVI 1032 in all epochs. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Dall'Osso S.,University of Tubingen | Giacomazzo B.,University of Trento | Giacomazzo B.,National Institute of Nuclear Physics, Italy | Perna R.,State University of New York at Stony Brook | Stella L.,National institute for astrophysics
Astrophysical Journal | Year: 2015

Binary neutron star (NS) mergers are among the most promising sources of gravitational waves (GWs), as well as candidate progenitors for short gamma-ray bursts (SGRBs). Depending on the total initial mass of the system and the NS equation of state (EOS), the post-merger phase can be characterized by a prompt collapse to a black hole or by the formation of a supramassive NS, or even a stable NS. In the latter cases of post-merger NS (PMNS) formation, magnetic field amplification during the merger will produce a magnetar and induce a mass quadrupole moment in the newly formed NS. If the timescale for orthogonalization of the magnetic symmetry axis with the spin axis is smaller than the spindown time, the NS will radiate its spin down energy primarily via GWs. Here we study this scenario for the various outcomes of NS formation: we generalize the set of equilibrium states for a twisted torus magnetic configuration to include solutions that, for the same external dipolar field, carry a larger magnetic energy reservoir; we hence compute the magnetic ellipticity for such configurations, and the corresponding strength of the expected GW signal as a function of the relative magnitude of the dipolar and toroidal field components. The relative number of GW detections from PMNSs and from binary NSs is a very strong function of the NS EOS, being higher (∼1%) for the stiffest EOSs and negligibly small for the softest ones. For intermediate-stiffness EOSs, such as the n = 4/7 polytrope recently used by Giacomazzo and Perna or the GM1 used by Lasky et al., the relative fraction is ∼0.3%; correspondingly, we estimate a GW detection rate from stable PMNSs of ∼0.1-1 yr-1 with advanced detectors, and of ∼100-1000 yr-1 with detectors of third generation such as the Einstein Telescope. Measurement of such GW signals would provide constraints on the NS EOS and, in connection with an SGRB, on the nature of the binary progenitors giving rise to these events. © 2015. The American Astronomical Society. All rights reserved.

Turrini D.,National institute for astrophysics | Svetsov V.,Russian Academy of Sciences
Life | Year: 2014

The asteroid (4) Vesta, parent body of the Howardite-Eucrite-Diogenite meteorites, is one of the first bodies that formed, mostly from volatile-depleted material, in the Solar System. The Dawn mission recently provided evidence that hydrated material was delivered to Vesta, possibly in a continuous way, over the last 4 Ga, while the study of the eucritic meteorites revealed a few samples that crystallized in presence of water and volatile elements. The formation of Jupiter and probably its migration occurred in the period when eucrites crystallized, and triggered a phase of bombardment that caused icy planetesimals to cross the asteroid belt. In this work, we study the flux of icy planetesimals on Vesta during the Jovian Early Bombardment and, using hydrodynamic simulations, the outcome of their collisions with the asteroid. We explore how the migration of the giant planet would affect the delivery of water and volatile materials to the asteroid and we discuss our results in the context of the geophysical and collisional evolution of Vesta. In particular, we argue that the observational data are best reproduced if the bulk of the impactors was represented by 1-2 km wide planetesimals and if Jupiter underwent a limited (a fraction of au) displacement. © 2014 by the authors; licensee MDPI, Basel, Switzerland.

Diolaiti E.,National institute for astrophysics
3rd AO4ELT Conference - Adaptive Optics for Extremely Large Telescopes | Year: 2013

The phase A conceptual design of the Multi-Conjugate Adaptive Optics module for the European Extremely Large Telescope has been developed to provide uniform adaptive optics compensation over an extended field of view in the near infrared with high sky coverage. The module design is based on the use of laser and natural guide stars and multiple deformable mirrors. An overview of the phase A design is given. The on-going technical activities in preparation for the project phase B are described.

Renzini A.,National institute for astrophysics | Peng Y.-J.,University of Cambridge
Astrophysical Journal Letters | Year: 2015

The main sequence (MS) of star-forming (SF) galaxies plays a fundamental role in driving galaxy evolution and our efforts to understand it. However, different studies find significant differences in the normalization, slope, and shape of the MS. These discrepancies arise mainly from the different selection criteria adopted to isolate SF galaxies, which may include or exclude galaxies with a specific star formation rate (SFR) substantially below the MS value. To obviate this limitation of all current criteria, we propose an objective definition of the MS that does not rely at all on a pre-selection of SF galaxies. Constructing the 3D SFR-mass-number plot, the MS is then defined as the ridge line of the SF peak, as illustrated with various figures. The advantages of such a definition are manifold. If generally adopted, it will facilitate the inter-comparison of results from different groups using the same SFR and stellar mass diagnostics, or it will highlight the relative systematics of different diagnostics. All of this could help to understand MS galaxies as systems in a quasi-steady state equilibrium and would also provide a more objective criterion for identifying quenching galaxies. © 2015. The American Astronomical Society. All rights reserved.

Fleck B.,NASA | Couvidat S.,Stanford University | Straus T.,National institute for astrophysics
Solar Physics | Year: 2011

The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) is designed to study oscillations and the magnetic field in the solar photosphere. It observes the full solar disk in the Fe i absorption line at 6173 Å. We use the output of a high-resolution, 3D, time-dependent, radiation-hydrodynamic simulation based on the CO5BOLD code to calculate profiles F(λ,x,y,t) for the Fe i 6173 Å line. The emerging profiles F(λ,x,y,t) are multiplied by a representative set of HMI filter-transmission profiles Ri(λ, 1≤i≤6) and filtergrams Ii(x,y,t; 1≤i≤6) are constructed for six wavelengths. Doppler velocities VHMI(x,y,t) are determined from these filtergrams using a simplified version of the HMI pipeline. The Doppler velocities are correlated with the original velocities in the simulated atmosphere. The cross-correlation peaks near 100 km, suggesting that the HMI Doppler velocity signal is formed rather low in the solar atmosphere. The same analysis is performed for the SOHO/MDI Ni i line at 6768 Å. The MDI Doppler signal is formed slightly higher at around 125 km. Taking into account the limited spatial resolution of the instruments, the apparent formation height of both the HMI and MDI Doppler signal increases by 40 to 50 km. We also study how uncertainties in the HMI filter-transmission profiles affect the calculated velocities. © 2011 Springer Science+Business Media B.V.

Risaliti G.,National institute for astrophysics | Risaliti G.,Harvard - Smithsonian Center for Astrophysics | Elvis M.,Harvard - Smithsonian Center for Astrophysics | Bianchi S.,Third University of Rome | Matt G.,Third University of Rome
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2010

We present a Chandra monitoring campaign of the highly variable Seyfert galaxy UGC 4203 (the 'Phoenix Galaxy') which revealed variations in the X-ray absorbing column density on time-scales of 2 weeks. This is the third, clear case, after NGC 1365 and NGC 7582, of dramatic NH. variability on short time-scales observed in a 'changing look' source, i.e. an active galactic nuclei (AGN) observed in the past in both a reflection-dominated and a Compton-thin state. The inferred limits on the distance of the X-ray absorber from the centre suggest that the X-ray 'torus' could be one and the same with the broad emission line region. This scenario, first proposed for an 'ad hoc' picture for NGC 1365, may be the common structure of the circumnuclear medium in AGN. © 2010 The Authors. Journal compilation © 2010 RAS.

Brown S.,CSIRO | Emerick A.,University of Minnesota | Rudnick L.,University of Minnesota | Brunetti G.,National institute for astrophysics
Astrophysical Journal Letters | Year: 2011

We derive the best characterization to date of the properties of radio quiescent massive galaxy clusters through a statistical analysis of their average synchrotron emissivity. We stacked 105 radio images of clusters from the 843MHz Sydney University Molonglo Sky Survey, all with LX > 1044ergs-1 and redshifts z < 0.2, after removing point-source contamination and rescaling to a common physical size. Each stacked cluster individually shows no significant large-scale diffuse radio emission at current sensitivity levels. Stacking of sub-samples leads to the following results: (1) clusters with LX > 3 × 1044ergs -1 show a 6σ detection of Mpc-scale diffuse emission with a 1.4GHz luminosity of (2.4 ± 0.4) ×1023WHz-1. This is 1.5-2 times lower than the upper limits for radio quiescent clusters from the GMRT Radio Halo Survey and is the first independent confirmation of radio halo bi-modality. (2) Clusters with low X-ray concentrations have a mean radio luminosity (2.6 ± 0.6 × 1023WHz-1) that is at least twice that of high X-ray concentration clusters, and (3) both of these detections are likely close to the low-level "off-state" of giant radio halos (GRHs) in most or all luminous X-ray clusters, and not due to contributions from a much smaller subset of "on-state" GRHs following the radio/X-ray luminosity correlation. Upcoming deep radio surveys will conclusively distinguish between these two options. We briefly discuss possible origins for the "off-state" emission and its implications for magnetic fields in most or all luminous X-ray clusters. © 2011. The American Astronomical Society. All rights reserved.

Swindle R.,University of Hawaii at Manoa | Gal R.R.,University of Hawaii at Manoa | La Barbera F.,National institute for astrophysics | De Carvalho R.R.,National Institute for Space Research
Astronomical Journal | Year: 2011

We present robust statistical estimates of the accuracy of early-type galaxy stellar masses derived from spectral energy distribution (SED) fitting as functions of various empirical and theoretical assumptions. Using large samples consisting of 40,000 galaxies from the Sloan Digital Sky Survey (SDSS; ugriz), of which 5000 are also in the UKIRT Infrared Deep Sky Survey (YJHK), with spectroscopic redshifts in the range 0.05 ≤ z ≤ 0.095, we test the reliability of some commonly used stellar population models and extinction laws for computing stellar masses. Spectroscopic ages (t), metallicities (Z), and extinctions (AV ) are also computed from fits to SDSS spectra using various population models. These external constraints are used in additional tests to estimate the systematic errors in the stellar masses derived from SED fitting, where t, Z, and AV are typically left as free parameters. We find reasonable agreement in mass estimates among stellar population models, with variation of the initial mass function and extinction law yielding systematic biases on the mass of nearly a factor of two, in agreement with other studies. Removing the near-infrared bands changes the statistical bias in mass by only 0.06dex, adding uncertainties of 0.1dex at the 95% CL. In contrast, we find that removing an ultraviolet band is more critical, introducing 2σ uncertainties of 0.15dex. Finally, we find that the stellar masses are less affected by the absence of metallicity and/or dust extinction knowledge. However, there is a definite systematic offset in the mass estimate when the stellar population age is unknown, up to a factor of 2.5 for very old (12Gyr) stellar populations. We present the stellar masses for our sample, corrected for the measured systematic biases due to photometrically determined ages, finding that age errors produce lower stellar masses by 0.15dex, with errors of 0.02dex at the 95% CL for the median stellar age subsample. © 2011 The American Astronomical Society. All rights reserved.

Caputo F.,National institute for astrophysics
Astrophysics and Space Science | Year: 2012

RR Lyrae variables play an important role in several fields of stellar evolution and cosmology, moreover, they are the most popular primary standard candles for Population II stellar systems. In this paper, their properties are examined within the framework of modern computations of stellar evolution and pulsation models in order to discuss their use as distance indicators. The comparison between selected observed data and predicted relations, for the determination of both apparent and intrinsic distance moduli, is also presented. © 2011 Springer Science+Business Media B.V.

Gupta A.,Ohio State University | Mathur S.,Ohio State University | Krongold Y.,National Autonomous University of Mexico | Nicastro F.,Harvard - Smithsonian Center for Astrophysics | And 2 more authors.
Astrophysical Journal Letters | Year: 2012

Most of the baryons from galaxies have been "missing" and several studies have attempted to map the circumgalactic medium (CGM) of galaxies in their quest. We report on X-ray observations made with the Chandra X-Ray Observatory probing the warm-hot phase of the CGM of our Milky Way at about 106K. We detect O VII and O VIII absorption lines at z = 0 in extragalactic sight lines and measure accurate column densities using both Kα and Kβ lines of O VII. We then combine these measurements with the emission measure of the Galactic halo from literature to derive the density and the path length of the CGM. We show that the warm-hot phase of the CGM is massive, extending over a large region around the Milky Way, with a radius of over 100kpc. The mass content of this phase is over 10 billion solar masses, many times more than that in cooler gas phases and comparable to the total baryonic mass in the disk of the Galaxy. The missing mass of the Galaxy appears to be in this warm-hot gas phase. © © 2012. The American Astronomical Society. All rights reserved.

Consolini G.,National institute for astrophysics | De Michelis P.,Italian National Institute of Geophysics and Volcanology
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2014

The present study is focused on the emergence of dynamical complexity in the Earth's magnetospheric dynamics during magnetic storms as monitored by SYM-H index. A long time series of SYM-H index covering the period from January 2000 to December 2004 is analyzed using a quite novel technique, the permutation entropy analysis. We show that the normalized permutation entropy values of the SYM-H time series decrease during geomagnetic disturbed periods revealing a gradual increase in the temporal correlation of the fluctuations which generates a gradual increase in the complexity degree of the magnetosphere response to the solar wind magnetic field and plasma parameter changes. These large changes in the normalized permutation entropy values and complexity degree observed during the disturbed periods can be interpreted as the signature of dynamical phase transitions happening in proximity to the occurrence of geomagnetic storms and substorms confirming results previously found using different methods. The dependence of the degree of complexity on both the magnitude of the geomagnetic disturbance and the IMF By GSM and Bz GSM components is investigated and discussed. © 2013 Elsevier Ltd.

Cantiello M.,National institute for astrophysics
Astrophysics and Space Science | Year: 2012

The analysis of deep imaging data of bright elliptical galaxies is capable of providing fundamental information on the stellar content and the distance of the target, via the Surface Brightness Fluctuation method (SBF hereafter). Here, I present the study of the properties of two ellipticals in the Virgo cluster, NGC 4621 and NGC 4374, based on deep BVR imaging data obtained with the FORS2 camera at the VLT. The V and R SBF measures are used to get accurate distances of the targets. In addition, since both galaxies hosted type Ia Supernova events, I also compare the new SBF distances with the ones based on SNe Ia lightcurve analysis. In all cases SBF distances agree well with distances obtained by other distance indicators. For what concerns stellar population analysis, I present a detailed comparison between SBF data and models to constrain the properties of the dominant stellar components. Among the other results, the measures presented here seem to suggest that the B-band SBF can be reconciled to model predictions only through the presence of a percentage of hot-HB stars "polluting" the old and metal rich dominant stellar population. © 2012 Springer Science+Business Media B.V.

Richichi A.,National Astronomical Research Institute of Thailand | Fors O.,University of Barcelona | Cusano F.,National institute for astrophysics | Moerchen M.,European Southern Observatory
Astrophysical Journal, Supplement Series | Year: 2012

Calibration is one of the long-standing problems in optical interferometric measurements, particularly with long baselines which demand stars with angular sizes on the milliarcsecond scale and no detectable companions. While systems of calibrators have been generally established for the near-infrared in the bright source regime (K ≲ 3mag), modern large interferometers are sensitive to significantly fainter magnitudes. We aim to provide a list of sources found to be unresolved from direct observations with high angular resolution and dynamic range, which can be used to choose interferometric calibrators. To this purpose, we have used a large number of lunar occultations recorded with the ISAAC instrument at the Very Large Telescope to select sources found to be unresolved and without close companions. An algorithm has been used to determine the limiting angular resolution achieved for each source, taking into account a noise model built from occulted and unocculted portions of the light curves. We have obtained upper limits on the angular sizes of 556 sources, with magnitudes ranging from K s 4 to 10, with a median of 7.2mag. The upper limits on possible undetected companions (within 0.″5) range from K s 8 to 13, with a median of 11.5mag. One-third of the sources have angular sizes ≤1 mas, and two-thirds have sizes ≤2 mas. This list of unresolved sources matches well the capabilities of current large interferometric facilities. We also provide available cross-identifications, magnitudes, spectral types, and other auxiliary information. A fraction of the sources are found to be potentially variable. The list covers parts of the Galactic Bulge and in particular the vicinity of the Galactic Center, where extinction is very significant and traditional lists of calibrators are often insufficient. © 2012. The American Astronomical Society. All rights reserved..

He J.-H.,National institute for astrophysics | Wang B.,Shanghai JiaoTong University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We reconstruct an f(R) gravity model that gives rise to the particular ΛCDM background evolution of the Universe. We find well-defined, real-valued analytical forms for the f(R) model to describe the Universe both in the early epoch from the radiation to matter dominated eras and the late time acceleration period. We further examine the viability of the derived f(R) model and find that it is viable to describe the evolution of the Universe in the past and the future singularity does not exist in the Lagrangian. © 2013 American Physical Society.

Altamirano D.,University of Amsterdam | Belloni T.,National institute for astrophysics
Astrophysical Journal Letters | Year: 2012

We report the discovery of 8.5σ high-frequency quasi-periodic oscillations (HFQPOs) at 66Hz in the Rossi X-ray Timing Explorer data of the black hole candidate IGRJ17091-3624, a system whose X-ray properties are very similar to those of microquasar GRS1915+105. The centroid frequency of the strongest peak is 66Hz, its quality factor above five, and its rms is between 4% and 10%. We found a possible additional peak at 164Hz when selecting a subset of the data; however, at the 4.5σ level we consider this detection marginal. These QPOs have hard spectrum and are stronger in observations performed between 2011 September and October, during which IGRJ17091-3624 displayed for the first time light curves that resemble those of the γ variability class in GRS1915+105. We find that the 66Hz QPO is also present in previous observations (4.5σ), but only when averaging 235ks of relatively high count rate data. The fact that the HFQPOs frequency in IGRJ17091-3624 matches surprisingly well with that seen in GRS1915+105 raises questions on the mass scaling of QPOs frequency in these two systems. We discuss some possible interpretations; however, they all strongly depend on the distance and mass of IGRJ17091-3624, both completely unconstrained today. © 2012 The American Astronomical Society. All rights reserved.

Villata M.,National institute for astrophysics
Astrophysics and Space Science | Year: 2012

The unexpected discovery of the accelerated cosmic expansion in 1998 has filled the Universe with the embarrassing presence of an unidentified "dark energy", or cosmological constant, devoid of any physical meaning. While this standard cosmology seems to work well at the global level, improved knowledge of the kinematics and other properties of our extragalactic neighborhood indicates the need for a better theory. We investigate whether the recently suggested repulsive-gravity scenario can account for some of the features that are unexplained by the standard model. Through simple dynamical considerations, we find that the Local Void could host an amount of antimatter (~5×10 15 M ⊙) roughly equivalent to the mass of a typical supercluster, thus restoring the matter-antimatter symmetry. The antigravity field produced by this "dark repulsor" can explain the anomalous motion of the Local Sheet away from the Local Void, as well as several other properties of nearby galaxies that seem to require void evacuation and structure formation much faster than expected from the standard model. At the global cosmological level, gravitational repulsion from antimatter hidden in voids can provide more than enough potential energy to drive both the cosmic expansion and its acceleration, with no need for an initial "explosion" and dark energy. Moreover, the discrete distribution of these dark repulsors, in contrast to the uniformly permeating dark energy, can also explain dark flows and other recently observed excessive inhomogeneities and anisotropies of the Universe. © 2012 Springer Science+Business Media B.V.

Foschini L.,National institute for astrophysics
Research in Astronomy and Astrophysics | Year: 2012

The effect of the observed continuum emitted from a relativistic jet on the measurement of the full width at half maximum (FWHM) of an emission line is analyzed. If the jet contribution is not properly subtracted, the FWHM of the line could seem narrower than it should. The cases of an emission line detected in BL Lac objects and γ-ray Narrow-Line Seyfert 1 galaxies (γ-NLS1s) are addressed. It is shown that the smallness of the observed FWHM of the Lyα lines detected in three well-known BL Lacs is an effect due to the combined action of both the relativistic jet and a weak accretion disk. Once the Doppler boosting effect of the jet continuum is removed, the intrinsic FWHM values of the lines are found to be in the usual range. By contrast, the narrow permitted lines in γ-NLS1s are really narrow, since the disk and the lines are much more powerful. This also confirms that γ-NLS1 is really a new class of γ-ray emitting AGN, different from blazars and radio galaxies. © 2012 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd.

De Lucia G.,National institute for astrophysics
Astronomische Nachrichten | Year: 2012

Our home galaxy - the Milky Way - is a fairly large spiral galaxy, prototype of the most common morphological class in the local Universe. Although being only a galaxy, it is the only one that can be studied in unique detail: for the Milky Way and for a number of members of the Local Group, a wealth of observational data is available about the ages and chemical abundances of their stars. Much more information is expected to come in the next few years, from ongoing and planned spectroscopic and astrometric surveys, providing a unique benchmark for modern theories of galaxy formation. In this review, I will summarize recent results on the formation of our Milky Way, its stellar halo, and its satellite galaxies. I will focus, in particular, on results obtained in the framework of hybrid models of galaxy formation, and refer to other reviews in this issue for studies based on hydrodynamical simulations © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Campana S.,National institute for astrophysics | Immler S.,NASA | Immler S.,University of Maryland University College
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

The Type IIb supernova (SN) 2011dh exploded in the nearby galaxy M51 (the Whirlpool galaxy) and provides us with one of the best laboratories to study early high-energy emission from SNe. We give here a comprehensive view of the X-ray properties of SN 2011dh from the analyses of two pointed XMM-Newton early observations as well as the full Swift X-ray Telescope (XRT) data set (163 ks). Due to the high XMM-Newton throughput, we were able to satisfactorily fit the X-ray spectrum with two hot diffuse gas components including an additional absorption component to our Galaxy. A power-law model provided a worse description of the data. In addition, the early Swift XRT light curve hints of a flux excess at early times (≲3 d), consistent with the adiabatic cooling of stellar's photosphere a few days after the shock breakout. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Di Serego Alighieri S.,National institute for astrophysics
International Journal of Modern Physics D | Year: 2015

Possible violations of fundamental physical principles, e.g. the Einstein equivalence principle on which all metric theories of gravity are based, including general relativity (GR), would lead to a rotation of the plane of polarization for linearly polarized radiation traveling over cosmological distances, the so-called cosmic polarization rotation (CPR). We review here the astrophysical tests which have been carried out so far to check if CPR exists. These are using the radio and ultraviolet polarization of radio galaxies and the polarization of the cosmic microwave background (both E-mode and B-mode). These tests so far have been negative, leading to upper limits of the order of one degree on any CPR angle, thereby increasing our confidence in those physical principles, including GR. We also discuss future prospects in detecting CPR or improving the constraints on it. © 2015 World Scientific Publishing Company.

Ghisellini G.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

The matter content of extragalactic relativistic jets is still an unsolved issue. There are strong arguments against pure electron-positron pair jets, but pairs could outnumber the electrons associated with protons by a factor of 10-20. This impacts on the estimate of the jet kinetic power, by reducing it by the same factor, and on the total energy delivered to leptons by the particle acceleration mechanism. Pairs cannot be created in the same jet zone responsible for the high-energy γ-ray emission we see in blazars, because the reprocessing of the created pairs would overproduce the X-ray flux. Copious pair creation could occur in the inner zone of the still accelerating jet, where the bulk Lorentz factor is small. It is found that the inner zone can produce a sufficient number of pairs to replenish the zone of the jet where most of the luminosity is emitted, but only if the γ-ray luminosity of the inner jet is above 10 44 erg s -1 at ~1MeV. Since the beaming is modest, this emission can be observed at large viewing angles, and detected in radio galaxies and lobe-dominated quasars at the flux level of 10 -12- 10 -11 erg cm -2 s -1 for a source at a redshift z = 0.1. © 2012 The Author Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Zanni C.,National institute for astrophysics
EPJ Web of Conferences | Year: 2014

Different classes of outflows are associated with the magnetospheric activity of accreting T Tauri protostars. Stellar winds are accelerated along the open field lines anchored in the stellar surface; disk winds (extended or X-type) can be launched along the open magnetic surfaces threading the accretion disk; another type of ejection can arise from the region of interaction of the closed magnetosphere with the accretion disk (magnetospheric ejections, conical winds), where the magnetic surfaces undergo quasiperiodic episodes of inflation and reconnection. In this chapter I will present the main dynamical properties of these different types of outflow. Two main issues will be addressed. First, I will try to understand if these ejection phenomena can account for the origin of the jets often observed in young forming stellar systems. Second, I will evaluate the impact of these outflows on the angular momentum evolution of the central protostar. © 2014 Owned by the authors.

D'elia V.,National institute for astrophysics
EAS Publications Series | Year: 2013

We analyze two X-shooter spectra of the GRB 120327A afterglow, acquired 2.1 and 30 hrs after the trigger. The ISM in the GRB host galaxy at z = 2.8145 is extremely rich in absorption features, with three components contributing to the line profiles. The hydrogen column density associated with GRB 120327A is log NHI / cm2 = 22.01 ± 0.09, and the metallicity of the host galaxy is in the range [X/H] = - 1.7 to - 1 with respect to the solar values, i.e., a typical value for a GRB host galaxy. In addition to the ground state lines, we detect in the first observation several excited absorption features, which disappeared in the second observation. Using these features, we derive that component I is at dI = 200+100 -60 \hbox{$d-I = 200^{+100}-{-60}$} d I = 20 0 -60 + 100 pc from the GRB, while component II is located closer, at dII = 100 +40 30 \hbox{$d-{II} = 100^{+40}-{30}$} d II = 10 0 30 + 40 pc. These values are among the lowest found in GRBs. Comparing the abundances with star formation history models, we find that the GRB 120327A host galaxy abundances are compatible with a star formation efficiency of 10 Gyr-1, typical of spheroids (elliptical or bulge). © EAS, EDP Sciences 2013.

Costa E.,National institute for astrophysics
EAS Publications Series | Year: 2013

Polarimetry is expected to play a major role as a diagnostic tool for GRBs. Techniques and methods for X/Gamma ray polarimetry are reviewed including the specific problems related to the transient nature of the sources. Optical data do not encourage optimistic predictions on polarimetry of afterglows. I review some of the existing and proposed experiments for the prompt and discuss the existing results. © EAS, EDP Sciences 2013.

Maoz D.,Tel Aviv University | Mannucci F.,National institute for astrophysics | Mannucci F.,Harvard - Smithsonian Center for Astrophysics
Publications of the Astronomical Society of Australia | Year: 2012

The identity of the progenitor systems of type-Ia supernovae (SNe Ia) is a major unsolved problem in astrophysics. SN Ia rates are providing some striking clues. We review the basics of SN rate measurement, preach about some sins of SN rate measurement and analysis, and illustrate one of these sins with an analogy about Martian scientists. We review the recent progress in measuring SN Ia rates in various environments and redshifts, and their use to reconstruct the SN Ia delay-time distribution (DTD) - the SN rate versus time that would follow a hypothetical brief burst of star formation. A good number of DTD measurements, using a variety of methods, appear to be converging. At delays 1t10Gyr, these measurements show a similar, ∼t -1, power-law shape. The DTD peaks at the shortest delays probed. This result supports the idea of a double-degenerate progenitor origin for SNe Ia. Single-degenerate progenitors may still play a role in producing short-delay SNe Ia, or perhaps all SNe Ia, if the red-giant donor channel is more efficient than is found by most theoretical models. The DTD normalization enjoys fairly good agreement (though perhaps some tension), among the various measurements, with a Hubble time-integrated DTD value of about 21 SNe Ia per 1000M ⊙ (stellar mass formed with a lowmass turnover initial mass function). The local WD binary population suggests that the WD merger rate can explain the Galactic SN Ia rate, but only if sub-Chandra mergers lead to SN Ia events. We point to some future directions that should lead to progress in the field, including measurement of the bivariate (delay and stretch) SN Ia response function. © 2012 Astronomical Society of Australia.

Kravtsov A.V.,University of Chicago | Borgani S.,University of Trieste | Borgani S.,National institute for astrophysics | Borgani S.,National Institute of Nuclear Physics, Italy
Annual Review of Astronomy and Astrophysics | Year: 2012

Formation of galaxy clusters corresponds to the collapse of the largest gravitationally bound overdensities in the initial density field and is accompanied by the most energetic phenomena since the Big Bang and by the complex interplay between gravity-induced dynamics of collapse and baryonic processes associated with galaxy formation. Galaxy clusters are, thus, at the cross-roads of cosmology and astrophysics and are unique laboratories for testing models of gravitational structure formation, galaxy evolution, thermodynamics of the intergalactic medium, and plasma physics. At the same time, their large masses make them a useful probe of growth of structure over cosmological time, thus providing cosmological constraints that are complementary to other probes. In this review, we describe our current understanding of cluster formation: from the general picture of collapse from initial density fluctuations in an expanding Universe to detailed simulations of cluster formation including the effects of galaxy formation. We outline both the areas in which highly accurate predictions of theoretical models can be obtained and areas where predictions are uncertain due to uncertain physics of galaxy formation and feedback. The former includes the description of the structural properties of the dark matter halos hosting clusters, their mass function, and clustering properties. Their study provides a foundation for cosmological applications of clusters and for testing the fundamental assumptions of the standard model of structure formation. The latter includes the description of the total gas and stellar fractions and the thermodynamical and nonthermal processes in the intracluster plasma. Their study serves as a testing ground for galaxy formation models and plasma physics. In this context, we identify a suitable radial range where the observed thermal properties of the intracluster plasma exhibit the most regular behavior and, thus, can be used to define robust observational proxies for the total cluster mass. Finally, we discuss the formation of clusters in nonstandard cosmological models, such as non-Gaussian models for the initial density field and models with modified gravity, along with prospects for testing these alternative scenarios with large cluster surveys in the near future. Copyright © 2012 by Annual Reviews.

Prokhorov D.A.,Stanford University | Colafrancesco S.,University of Witwatersrand | Colafrancesco S.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

Clusters of galaxies are mainly formed by merging of smaller structures, according to the standard cosmological scenario. If the mass of a substructure is>10 per cent of that of a galaxy cluster, the temperature distribution of the intracluster medium (ICM) in a merging cluster becomes inhomogeneous. Various methods have been used to derive the two-dimensional projected temperature distribution of the ICM. However, methods for studying temperature distribution along the line of sight through the cluster were absent. In this Letter, we present the first measurement of the temperature standard deviation along the line of sight, using as a reference case the multifrequency Sunyaev-Zel'dovich measurements of the Bullet Cluster. We find that the value of the temperature standard deviation is high and equals to (10.6 ± 3.8) keV in the Bullet Cluster. This result shows that the temperature distribution in the Bullet Cluster is strongly inhomogeneous along the line ofsight and provides a new method for studying galaxy clusters in depth. © 2012 The Authors, MNRAS 424, L49-L53 Monthly Notices of the Royal Astronomical Society. © 2012 RAS.

Alighieri S.D.S.,National institute for astrophysics | Ni W.-T.,National Tsing Hua University | Pan W.-P.,National Tsing Hua University
Astrophysical Journal | Year: 2014

SPTpol, POLARBEAR, and BICEP2 have recently measured the cosmic microwave background (CMB) B-mode polarization in various sky regions of several tens of square degrees and obtained BB power spectra in the multipole range 20-3000, detecting the components due to gravitational lensing and to inflationary gravitational waves. We analyze jointly the results of these three experiments and propose modifications to their analyses of the spectra to include in the model, in addition to the gravitational lensing and the inflationary gravitational wave components, and also the effects induced by the cosmic polarization rotation (CPR), if it exists within current upper limits. Although in principle our analysis would also lead to new constraints on CPR, in practice these can only be given on its fluctuations 〈δα 2〉, since constraints on its mean angle are inhibited by the derotation which is applied by current CMB polarization experiments, in order to cope with the insufficient calibration of the polarization angle. The combined data fits from all three experiments (with 29% CPR-SPTpol correlation, depending on the theoretical model) gives the constraint 〈δα 2〉1/2 < 27.3 mrad (1.°56), with r = 0.194 ± 0.033. These results show that the present data are consistent with no CPR detection and the constraint on CPR fluctuation is about 1.°5. This method of constraining the CPR is new, is complementary to previous tests, which use the radio and optical/UV polarization of radio galaxies and the CMB E-mode polarization, and adds a new constraint for the sky areas observed by SPTpol, POLARBEAR, and BICEP2. © 2014. The American Astronomical Society. All rights reserved.

Correnti M.,US Space Telescope Science Institute | Goudfrooij P.,US Space Telescope Science Institute | Kalirai J.S.,US Space Telescope Science Institute | Kalirai J.S.,University of Baltimore | And 3 more authors.
Astrophysical Journal | Year: 2014

We use the Wide Field Camera 3 on board the Hubble Space Telescope (HST) to obtain deep, high-resolution images of two intermediate-age star clusters in the Large Magellanic Cloud of relatively low mass (104M ⊙) and significantly different core radii, namely NGC 2209 and NGC 2249. For comparison purposes, we also reanalyzed archival HST images of NGC 1795 and IC 2146, two other relatively low-mass star clusters. From the comparison of the observed color-magnitude diagrams with Monte Carlo simulations, we find that the main-sequence turnoff (MSTO) regions in NGC 2209 and NGC 2249 are significantly wider than that derived from simulations of simple stellar populations, while those in NGC 1795 and IC 2146 are not. We determine the evolution of the clusters' masses and escape velocities from an age of 10 Myr to the present age. We find that differences among these clusters can be explained by dynamical evolution arguments if the currently extended clusters (NGC 2209 and IC 2146) experienced stronger levels of initial mass segregation than the currently compact ones (NGC 2249 and NGC 1795). Under this assumption, we find that NGC 2209 and NGC 2249 have estimated escape velocities, V esc≳ 15 km s-1at an age of 10 Myr, large enough to retain material ejected by slow winds of first-generation stars, while the two clusters that do not feature extended MSTOs have V esc≲ 12 km s-1at that age. These results suggest that the extended MSTO phenomenon can be better explained by a range of stellar ages rather than a range of stellar rotation velocities or interacting binaries. © 2014. The American Astronomical Society. All rights reserved..

Martel H.,Laval University | Robichaud F.,Laval University | Barai P.,National institute for astrophysics
Astrophysical Journal | Year: 2014

Using a large N-body cosmological simulation combined with a subgrid treatment of galaxy formation, merging, and tidal destruction, we study the formation and evolution of the galaxy and cluster population in a comoving volume (100 Mpc)3 in a ΛCDM universe. At z = 0, our computational volume contains 1788 clusters with mass M cl > 1.1 × 1012 M ⊙, including 18 massive clusters with M cl > 1014 M ⊙. It also contains 1, 088, 797 galaxies with mass M gal ≥ 2 × 109 M ⊙ and luminosity L > 9.5 × 105 L. For each cluster, we identified the brightest cluster galaxy (BCG). We then computed two separate statistics: the fraction f BNC of clusters in which the BCG is not the closest galaxy to the center of the cluster in projection, and the ratio Δv/σ, where Δv is the difference in radial velocity between the BCG and the whole cluster and σ is the radial velocity dispersion of the cluster. We found that f BNC increases from 0.05 for low-mass clusters (M cl ∼ 1012 M ⊙) to 0.5 for high-mass clusters (M cl > 10 14 M ⊙) with very little dependence on cluster redshift. Most of this result turns out to be a projection effect and when we consider three-dimensional distances instead of projected distances, f BNC increases only to 0.2 at high-cluster mass. The values of Δv/σ vary from 0 to 1.8, with median values in the range 0.03-0.15 when considering all clusters, and 0.12-0.31 when considering only massive clusters. These results are consistent with previous observational studies and indicate that the central galaxy paradigm, which states that the BCG should be at rest at the center of the cluster, is usually valid, but exceptions are too common to be ignored. We built merger trees for the 18 most massive clusters in the simulation. Analysis of these trees reveal that 16 of these clusters have experienced 1 or several major or semi-major mergers in the past. These mergers leave each cluster in a non-equilibrium state, but eventually the cluster settles into an equilibrium configuration, unless it is disturbed by another major or semi-major merger. We found evidence that these mergers are responsible for the off-center positions and peculiar velocities of some BCGs. Our results thus support the merging-group scenario, in which some clusters form by the merging of smaller groups in which the galaxies have already formed, including the galaxy destined to become the BCG. Finally, we argue that f BNC is not a very robust statistics, as it is very sensitive to projection and selection effects, but that Δv/σ is more robust. Still, both statistics exhibit a signature of major mergers between clusters of galaxies. © 2014. The American Astronomical Society. All rights reserved.

Yacobi L.,Technion - Israel Institute of Technology | Guetta D.,Technion - Israel Institute of Technology | Guetta D.,National institute for astrophysics | Behar E.,Technion - Israel Institute of Technology
Astrophysical Journal | Year: 2014

The IceCube High-energy Neutrino Telescope has been collecting data since 2006. Conversely, hundreds of gamma-ray bursts (GRBs) have been detected by the GRB Monitor on board Fermi since its launch in 2008. So far no neutrino event has been associated with a GRB, despite many models predicting the generation of high-energy neutrinos through GRB photon interaction with PeV protons in the GRB jet. We use the non-detection of neutrinos to constrain the hadronic content of GRB jets independent of jet model parameters. Assuming a generic particle spectrum of E -αwith α = 2, we find that the ratio of the energy carried by pions to that in electrons has to be small f π/fe≲ 0.24 at 95% confidence level. A distribution of spectral slopes can lower f π/feby orders of magnitude. Another limit, independent of neutrinos, is obtained if one ascribes the measured Fermi/Large Area Telescope GeV gamma-ray emission to pair-photon cascades of high-energy photons resulting from (the same photon-hadronic interactions and subsequent) neutral pion decays. Based on the generally observed MeV-to-GeV GRB fluence ratio of ≈10, we show that f π/fe≲ 0.3. In some bursts, this ratio is as low as unity, f π/fe≲ 0.03. These findings add to mounting doubts regarding the presence of PeV protons in GRB jets. © 2014. The American Astronomical Society. All rights reserved..

Bandiera R.,National institute for astrophysics
Astronomische Nachrichten | Year: 2014

The number of known pulsar wind nebulae (PWNe) has recently increased considerably, and the majority of them are now middle-age objects. Recent studies have shown a clear correlation of both X-ray luminosity and size with the PWN age, but fail in providing a thorough explanation of the observed trends. Here I propose a different approach to these effects, based on the hypothesis that the observed trends do not simply reproduce the evolution of a "typical" PWN, but are a combined effect of PWNe evolving under different ambient conditions, the leading parameter being the ambient medium density. Using a simple analytic approach, I show that most middle-aged PWNe are more likely observable during the reverberation phase, and I succeed in reproducing trends consistent with those observed, provided that the evolution of the X-ray emitting electrons remains adiabatic over the whole reverberation phase. As a direct consequence, I show that the X-ray spectra of older PWNe should be harder, also consistent with observations. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Peng Y.-J.,ETH Zurich | Lilly S.J.,ETH Zurich | Renzini A.,National institute for astrophysics | Carollo M.,ETH Zurich
Astrophysical Journal | Year: 2014

Using our continuity approach, we explore the underlying connections between the evolution of the faint-end slope αs of the stellar mass function of star-forming galaxies, the logarithmic slope β of the specific star formation rate (sSFR)-mass relation, and the merging of galaxies. We derive analytically the consequences of the observed constancy of αs since redshifts of at least z ∼ 2. If the logarithmic slope β of the sSFR-mass relation is negative, then the faint-end slope αs should quickly diverge due to the differential mass increase of galaxies on the star-forming main sequence, and this will also quickly destroy the Schechter form of the mass function. This problem can be solved by removing low-mass galaxies by merging them into more massive galaxies. We quantify this process by introducing the specific merger mass rate (sMMR) as the specific rate of mass added to a given galaxy through mergers. For a modest negative value of β ∼ -0.1, an average sMMR ∼ 0.1 sSFR across the population is required to keep αs constant with epoch, as observed. This in turn implies a merger rate of ∼0.2 sSFR for major mergers, which is consistent with the available observational estimates. More negative values of β require higher sMMR and higher merger rates, and the steepening of the mass function becomes impossible to control for β < -(αs + 2). The close link that is required between the in situ sSFR and the sMMR probably arises because both are closely linked to the buildup of dark matter halos. These new findings further develop the formalism for the evolving galaxy population that we introduced earlier and show how striking symmetries in the galaxy population can emerge as the result of deep links between the physical processes involved. © 2014. The American Astronomical Society. All rights reserved.

Nusser A.,Asher Space Science Institute Technion | Davis M.,University of California at Berkeley | Branchini E.,Third University of Rome | Branchini E.,National institute for astrophysics
Astrophysical Journal | Year: 2014

There is an ∼150 km s-1 discrepancy between the measured motion of the Local Group (LG) of galaxies with respect to the cosmic microwave background and the linear theory prediction based on the gravitational force field of the large-scale structure in full-sky redshift surveys. We perform a variety of tests which show that the LG motion cannot be recovered to better than 150-200 km s-1 in amplitude and within 10° in direction. The tests rely on catalogs of mock galaxies identified in the Millennium simulation using semi-analytic galaxy formation models. We compare these results to the Ks = 11.75 Two-Mass Galaxy Redshift Survey, which provides the deepest and most complete all-sky spatial distribution of galaxies with spectroscopic redshifts available thus far. In our analysis, we use a new concise relation for deriving the LG motion and bulk flow from the true distribution of galaxies in redshift space. Our results show that the main source of uncertainty is the small effective depth of surveys like the Two-Mass Redshift Survey (2MRS), which prevents a proper sampling of the large-scale structure beyond ∼100 h -1 Mpc. Deeper redshift surveys are needed to reach the "convergence scale" of 250 h -1 Mpc in a ΛCDM universe. Deeper surveys would also mitigate the impact of the "Kaiser rocket" which, in a survey like 2MRS, remains a significant source of uncertainty. Thanks to the quiet and moderate density environment of the LG, purely dynamical uncertainties of the linear predictions are subdominant at the level of ∼90 km s-1. Finally, we show that deviations from linear galaxy biasing and shot noise errors provide a minor contribution to the total error budget. © 2014. The American Astronomical Society. All rights reserved..

Jones B.M.,University of Hawaii at Manoa | Kaiser R.I.,University of Hawaii at Manoa | Strazzulla G.,National institute for astrophysics
Astrophysical Journal | Year: 2014

Carbon dioxide (CO2) has been detected on the surface of several icy moons of Jupiter and Saturn via observation of the ν3 band with the Near-Infrared Mapping Spectrometer on board the Galileo spacecraft and the Visible-Infrared Mapping Spectrometer on board the Cassini spacecraft. Interestingly, the CO2 band for several of these moons exhibits a blueshift along with a broader profile than that seen in laboratory studies and other astrophysical environments. As such, numerous attempts have been made in order to clarify this abnormal behavior; however, it currently lacks an acceptable physical or chemical explanation. We present a rather surprising result pertaining to the synthesis of carbon dioxide in a polar environment. Here, carbonic acid was synthesized in a water (H2O)-carbon dioxide (CO2) (1:5) ice mixture exposed to ionizing radiation in the form of 5 keV electrons. The irradiated ice mixture was then annealed, producing pure carbonic acid which was then subsequently irradiated, recycling water and carbon dioxide. However, the observed carbon dioxide ν3 band matches almost exactly with that observed on Callisto; subsequent temperature program desorption studies reveal that carbon dioxide synthesized under these conditions remains in solid form until 160 K, i.e., the sublimation temperature of water. Consequently, our results suggest that carbon dioxide on Callisto as well as other icy moons is indeed complexed with water rationalizing the shift in peak frequency, broad profile, and the solid state existence on these relatively warm moons. © 2014. The American Astronomical Society. All rights reserved.

Muleri F.,National institute for astrophysics
Astrophysical Journal | Year: 2014

The measurement of linear polarization is one of the hot topics of high-energy astrophysics. Gas detectors based on the photoelectric effect have paved the way for the design of sensitive instruments, and mission proposals based on them have been presented in the last few years in the energy range from about 2 keV to a few tens of keV. In addition, a number of polarimeters based on Compton scattering are approved or being discussed for launch on board balloons or space satellites at higher energies. These instruments are typically dedicated to pointed observations with narrow field of view telescopes or collimators, but there are also projects aimed at the polarimetry of bright transient sources such as soft gamma repeaters or the prompt emission of gamma-ray bursts. Given the erratic appearance of such events in the sky, these polarimeters have large fields of view to catch a reasonable number of them, and as a result, photons may impinge on the detector off-axis. This dramatically changes the response of the instrument to polarization, regardless of whether photoabsorption or Compton scattering is involved. Instead of the simple cosine-squared dependence expected for polarized photons that are incident on-axis, the response is never purely cosinusoidal, and a systematic modulation also appears for unpolarized radiation. We investigate the origin of these differences and present an analytical treatment that proves that such systematic effects are actually a natural consequence of how current instruments operate. Our analysis provides the expected response of photoelectric or Compton polarimeters to photons impinging with any inclination and state of polarization. © 2014. The American Astronomical Society. All rights reserved..

Urpin V.,National institute for astrophysics | Urpin V.,National Institute of Nuclear Physics, Italy | Urpin V.,RAS Ioffe Physical - Technical Institute
Astronomy and Astrophysics | Year: 2012

Context. Magnetohydrodynamic (MHD) instabilities can play an important role in the structure and dynamics of the pulsar magnetosphere. Aims. We consider the instability caused by differential rotation that is suggested by many theoretical models. Methods. Stability is considered by means of a linear analysis within the frame of the force-free MHD. Results. We argue that differentially rotating magnetospheres are unstable for any particular geometry of the magnetic field and rotation law. The characteristic growth time of instability is of the order of the rotation period. The instability can lead to fluctuations of the emission and enhancement of diffusion in the magnetosphere. © 2012 ESO.

Petropoulou M.,Purdue University | Giannios D.,Purdue University | Dimitrakoudis S.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2014

The recent discovery of extragalactic PeV neutrinos opens a new window to the exploration of cosmic ray accelerators. The observed PeV neutrino flux is close to the Waxman-Bahcall upper bound implying that gamma-ray bursts (GRBs) may be the source of ultrahigh energy cosmic rays (UHECRs). Starting with the assumption of the GRB-UHECR connection, we show using both analytical estimates and numerical simulations that the observed neutrinos can originate at the jet as a result of photopion interactions with the following implications: the neutrino spectra are predicted to have a cut-off at energy ≳10 PeV; the dissipation responsible for the GRB emission and cosmic ray acceleration takes place at distances rdiss ≃3×1011-3× 1013 cm from the central engine; the Thomson optical depth at the dissipation region is τT ≃ 1; the jet carries a substantial fraction of its energy in the form of Poynting flux at the dissipation region, and has a Lorentz factor Γ ≃ 100-500. The non-detection of PeV neutrinos coincident with GRBs will indicate that GRBs are either poor cosmic accelerators or the dissipation takes place at small optical depths in the jet. ©2014 The Authors.

De Grijs R.,Peking University | Wicker J.E.,CAS National Astronomical Observatories | Bono G.,University of Rome Tor Vergata | Bono G.,National institute for astrophysics
Astronomical Journal | Year: 2014

The distance to the Large Magellanic Cloud (LMC) represents a key local rung of the extragalactic distance ladder yet the galaxy's distance modulus has long been an issue of contention, in particular in view of claims that most newly determined distance moduli cluster tightly - and with a small spread - around the "canonical" distance modulus, (m-M)0 = 18.50 mag. We compiled 233 separate LMC distance determinations published between 1990 and 2013. Our analysis of the individual distance moduli, as well as of their two-year means and standard deviations resulting from this largest data set of LMC distance moduli available to date, focuses specifically on Cepheid and RR Lyrae variable-star tracer populations, as well as on distance estimates based on features in the observational Hertzsprung-Russell diagram. We conclude that strong publication bias is unlikely to have been the main driver of the majority of published LMC distance moduli. However, for a given distance tracer, the body of publications leading to the tightly clustered distances is based on highly non-independent tracer samples and analysis methods, hence leading to significant correlations among the LMC distances reported in subsequent articles. Based on a careful, weighted combination, in a statistical sense, of the main stellar population tracers, we recommend that a slightly adjusted canonical distance modulus of (m-M)0 = 18.49 ± 0.09 mag be used for all practical purposes that require a general distance scale without the need for accuracies of better than a few percent. © 2014. The American Astronomical Society. All rights reserved.

Mei H.-H.,National Tsing Hua University | Ni W.-T.,National Tsing Hua University | Pan W.-P.,National Tsing Hua University | Xu L.,Dalian University of Technology | Alighieri S.D.S.,National institute for astrophysics
Astrophysical Journal | Year: 2015

Recently, ACTPol measured the cosmic microwave background (CMB) B-mode and E-mode polarizations and obtained TE, EE, BB, TB, and EB power spectra in the multipole range 2258725. In our previous paper (Paper I), we jointly analyzed the results of three experiments on the CMB B-mode polarizationSPTpol, POLARBEAR, and BICEP2to include in the model, in addition to the gravitational lensing and inflationary gravitational waves components, the fluctuation effects induced by cosmic polarization rotation (CPR) if it exists within the upper limits at the time. In this paper, we fit both the mean CPR angle ?α? and its fluctuation ?δα2? from the new ACTPol data, and update our fitting of CPR fluctuations using the BICEP2 data taking the new Planck dust measurement results into consideration. We follow the same method used in Paper I. The mean CPR angle is constrained from the EB correlation power spectra to α < 14 mrad (0°. 8) and the fluctuation (rms) is constrained from the BB correlation power spectra to ?δα2?1 2.29.3 mrad (1°. 68). Assuming that the polarization angle of Tau A does not change from 89.2 to 146 GHz, the ACTPol data give ?α? = 1.0 ± 0°.63. These results suggest that the inclusion of the present ACTPol data is consistent with no CPR detection. Using the new Planck dust measurement, we update our fits of the BICEP2 CPR fluctuation constraint to be 32.8 mrad (1°. 88). The joint ACTPol-BICEP2-POLARBEAR CPR fluctuation constraint is 23.7 mrad (1°. 36). © 2015. The American Astronomical Society. All rights reserved.

Ghisellini G.,National institute for astrophysics
Journal of High Energy Astrophysics | Year: 2015

I will review recent advances in the field of blazars, highlighting the contribution of Swift. Together with other operating satellites (most notably Fermi, but also AGILE, WISE, Planck) and ground based facilities such as Cherenkov telescopes, Swift was (and is) crucial for improving our understanding of blazars. The main advances in the blazar field made possible by Swift includes the opening of the time domain investigation, since there are several sources with hundreds of simultaneous optical, UV and X-ray data taken at different times; the possibility to measure the black hole mass in very powerful blazars, that show clear signs of accretion disk emission; the possibility to classify blazar candidates, through X-ray observations; the finding of the most powerful and distant blazars, emitting strongly in the hard X-ray band accessible to Swift/BAT. All these improvements had and have a great impact on our understanding on how relativistic jets are formed and emit, on their power, and on how the heavy black holes in these systems first formed and grew. © 2015 Elsevier B.V.

Bernardini M.G.,National institute for astrophysics
Journal of High Energy Astrophysics | Year: 2015

Newly-born millisecond magnetars are competing with black holes as source of the gamma-ray burst (GRB) power, mainly with their rotational energy reservoir. They may be formed both in the core-collapse of massive stars, and in the merger of neutron star or white dwarf binaries, or in the accretion-induced collapse of a white dwarf, being thus a plausible progenitor for long and short GRBs, respectively. In ten years of activity, Swift has provided compelling observational evidences supporting the magnetar central engine, as the presence of a plateau phase in the X-ray light curve, the extended emission in SGRBs and the precursor and flaring activity. We review the major observational evidences for the possible presence of a newly-born magnetar as the central engine for both long and short GRBs. We then discuss about the possibility that all GRBs are powered by magnetars, and we propose a unification scheme that accommodates both magnetars and black holes, connected to the different properties and energetics of GRBs. Since the central engine remains hidden from direct electromagnetic observations, we review the predictions for the GW emission from magnetars hosted from GRBs, and the observational perspectives with advanced interferometers. © 2015 Elsevier B.V.

Nusser A.,Asher Space Science Institute Technion | Branchini E.,Third University of Rome | Branchini E.,National Institute of Nuclear Physics, Italy | Branchini E.,National institute for astrophysics | Davis M.,University of California at Berkeley
Astrophysical Journal | Year: 2012

Given a redshift survey of galaxies with measurements of apparent magnitudes, we present a novel method for measuring the growth rate f(Ω) of cosmological linear perturbations. We use the galaxy distribution within the survey to solve for the peculiar velocity field which depends in linear perturbation theory on β = f(Ω)/b, where b is the bias factor of the galaxy distribution. The recovered line-of-sight peculiar velocities are subtracted from the redshifts to derive the distances, which thus allows an estimate of the absolute magnitude of each galaxy. A constraint on β is then found by minimizing the spread of the estimated magnitudes from their distribution function. We apply the method to the all sky K = 11.25 2MASS Redshift Survey and derive β = 0.35 0.1 at z 0, remarkably consistent with our previous estimate from the velocity-velocity comparison. The method could easily be applied to subvolumes extracted from the Sloan Digital Sky Survey to derive the growth rate at z 0.1. Further, it should also be applicable to ongoing and future spectroscopic redshift surveys to trace the evolution of f(Ω) to z 1. Constraints obtained from this method are entirely independent from those obtained from the two-dimensional distortion of ξ(s) and provide an important check on f(Ω), as alternative gravity models predict observable differences. © 2012 The American Astronomical Society. All rights reserved.

Andreon S.,National institute for astrophysics | Hurn M.,University of Bath
Statistical Analysis and Data Mining | Year: 2013

This review article considers some of the most common methods used in astronomy for regressing one quantity against another in order to estimate the model parameters or to predict an observationally expensive quantity using trends between object values. These methods have to tackle some of the awkward features prevalent in astronomical data, namely heteroscedastic (point-dependent) errors, intrinsic scatter, non-ignorable data collection and selection effects, data structure and non-uniform population (often called Malmquist bias), non-Gaussian data, outliers, and mixtures of regressions. We outline how least square fits, weighted least squares methods, Maximum Likelihood, survival analysis, and Bayesian methods have been applied in the astrophysics literature when one or more of these features is present. In particular we concentrate on errors-in-variables regression and we advocate Bayesian techniques. © 2012 Wiley Periodicals, Inc., A Wiley Company.

Crosta M.,National institute for astrophysics
Classical and Quantum Gravity | Year: 2011

Advancement in astronomical observations requires codification of light propagation and of the processes of its physical measurement at a high level of accuracy. This could unveil a new window of several subtle relativistic effects suffered by light while propagating. Indeed, light modeling and its subsequent detection should be conceived in a fully relativistic context, in order to interpret the outcome of the observing process in accordance with the geometrical environment affecting light propagation itself and the precepts of measurement. This paper deals with the complexity of such a topic by showing how the geometrical framework of RAMOD, a relativistic model initially developed for astrometric observations in the visible, constitutes an appropriate environment for back-tracing photons. Through gauging the energy content of a given gravitationally bound system, the geometrical aspects that match the required accuracy of present and future observational capabilities are evidenced. Then, by comparing different formulations of the null geodesic, their domain of validity within the given geometrical scheme is refined. Finally, by proving its ability in retrieving recent literature cases, RAMOD is promoted as a measurement-based general relativistic method for any present and future advancement in the light-tracing problem. © 2011 IOP Publishing Ltd.

Curir A.,National institute for astrophysics
Communications in Theoretical Physics | Year: 2011

The recent thermodynamical interpretation of the field equations of gravity is revisited and extended to the killing horizons linked to the rotation (Kerr black holes). An entropic force can be defined also for these horizons which are not event horizons but show thermodynamical features that in previous works were used to explain the rotational properties of Kerr solutions. Such entropic force is needed to describe the energetic processes, which do not change the usual thermal entropy of the rotating black hole (reversible transformations, superradiance). © 2011 Chinese Physical Society and IOP Publishing Ltd.

Tavecchio F.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2014

The peculiar high-energy emission spectrum of the so-called extreme BL Lacs (EHBL) challenges the standard emission models of blazars. Among the possible solutions, the so-called hadronic cascade scenario assumes that the observed high-energy radiation is produced in the intergalactic space through photo-hadronic reactions by ultra-high energy cosmic rays (UHECR) with energies up to 1019-20 eV beamed by the blazar jet. Under the assumption - implicit in this model - that the intrinsic high-energy synchrotron self-Compton emission of the blazar does not substantially contribute to the observed γ-ray spectrum, we derive constraints to the basic physical quantities of the jet and we compare them with the requirements of the hadronic cascade scenario. We found that, for a plausible range of relativistic jet Doppler factors (δ = 10-50), the maximum achievable energy of the accelerated protons can exceed 2 × 1019 eV with jet powers of the order of ≈1044 erg s-1, parameters compatible with the requests of the hadronic scenario even if EHBL are embedded in magnetic fields of cosmic filaments. We also discuss the consequences of our results for the possibility that local EHBL contribute to the observed UHECR. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.

Da Costa G.S.,Australian National University | Held E.V.,National institute for astrophysics | Saviane I.,European Southern Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present a detailed study of the strengths of the calcium triplet absorption lines in the spectra of a large sample of red giant members of the luminous outer Galactic halo globular cluster NGC 5824. The spectra were obtained with the FORS2 and GMOS-S multi-object spectrographs at the VLT and the Gemini-S telescope, respectively. By comparing the line strengths of the NGC 5824 stars with those for red giants in clusters with well-established abundances, we conclude that there is an intrinsic abundance dispersion in NGC 5824 characterized by an inter-quartile range in [Fe/H] of 0.10 dex and a total range of ∼0.3 dex. As for ω Cen and M22, the abundance distribution shows a steep rise on the metal-poor side and a shallower decline on the metal-rich side. There is also some indication that the distribution is not unimodal with perhaps three distinct abundance groupings present. NGC 5824 has a further unusual characteristic: the outer surface density profile shows no signs of a tidal cutoff. Instead, the profile has a power-law distribution with cluster stars detected to a radius exceeding 400 pc. We postulate that NGC 5824 may be the remnant nuclear star cluster of a now disrupted dwarf galaxy accreted during the formation of the Galaxy's halo. We further speculate that the presence of an intrinsic [Fe/H] spread is the characteristic that distinguishes former nuclear star clusters from other globular clusters. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Mosqueira I.,Search for Extraterrestrial Intelligence Institute | Estrada P.,Search for Extraterrestrial Intelligence Institute | Turrini D.,National institute for astrophysics
Space Science Reviews | Year: 2010

The origin of the regular satellites ties directly to planetary formation in that the satellites form in gas and dust disks around the giant planets and may be viewed as mini-solar systems, involving a number of closely related underlying physical processes. The regular satellites of Jupiter and Saturn share a number of remarkable similarities that taken together make a compelling case for a deep-seated order and structure governing their origin. Furthermore, the similarities in the mass ratio of the largest satellites to their primaries, the specific angular momenta, and the bulk compositions of the two satellite systems are significant and in need of explanation. Yet, the differences are also striking. We advance a common framework for the origin of the regular satellites of Jupiter and Saturn and discuss the accretion of satellites in gaseous, circumplanetary disks. Following giant planet formation, planetesimals in the planet's feeding zone undergo a brief period of intense collisional grinding. Mass delivery to the circumplanetary disk via ablation of planetesimal fragments has implications for a host of satellite observations, tying the history of planetesimals to that of satellitesimals and ultimately that of the satellites themselves. By contrast, irregular satellites are objects captured during the final stages of planetary formation or the early evolution of the Solar System; their distinct origin is reflected in their physical properties, which has implications for the subsequent evolution of the satellites systems. © 2010 Springer Science+Business Media B.V.

Wendt M.,University of Potsdam | Molaro P.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2012

Context. The variation of the dimensionless fundamental physical constant μ = m p/m e-the proton to electron mass ratio-can be constrained via observation of Lyman and Werner lines of molecular hydrogen in the spectra of damped Lyman alpha systems (DLAs) in the line of sight to distant QSOs. Aims. Our intention is to maximize the possible precision of quasar absorption spectroscopy with regard to the investigation of the variation of the proton-to-electron mass-ratio μ. The demand for precision requires an understanding of the errors involved and effective techniques to handle present systematic errors. Methods. An analysis based on UVES high resolution data sets of QSO 0347-383 and its DLA is put forward and new approaches to some of the steps involved in the data analysis are introduced. We apply corrections for the observed offsets between discrete spectra and for the first time we find indications for inter-order distortions. Results. Drawing on VLT-UVES observations of QSO 0347-383 in 2009 our analysis yields Δμ/μ = (4.3 ± 7.2) × 10 -6 at z abs = 3.025. Conclusions. Current analyzes tend to underestimate the impact of systematic errors. Based on the scatter of the measured redshifts and the corresponding low significance of the redshift-sensitivity correlation we estimate the limit of accuracy of line position measurements to ~220 m s -1, consisting of roughly 150 m s -1 due to the uncertainty of the absorption line fit and about 150 m s -1 allocated to systematics related to instrumentation and calibration. © 2012 ESO.

Aoki W.,Japan National Astronomical Observatory | Aoki W.,Graduate University for Advanced Studies | Beers T.C.,Michigan State University | Honda S.,Kyoto University | And 2 more authors.
Astrophysical Journal Letters | Year: 2010

We report the discovery of a cool metal-poor, main-sequence star exhibiting large excesses of r-process elements. This star is one of the two newly discovered cool subdwarfs (effective temperatures of 5000 K) with extremely low metallicity ([Fe/H] < -3) identified from follow-up high-resolution spectroscopy of metal-poor candidates from the Sloan Digital Sky Survey. SDSS J2357-0052 has [Fe/H]= -3.4 and [Eu/Fe]= +1.9, and exhibits a scaled solar r-process abundance pattern of heavy neutron-capture elements. This is the first example of an extremely metal-poor, main-sequence star showing large excesses of r-process elements; all previous examples of the large r-process-enhancement phenomena have been associated with metal-poor giants. The metallicity of this object is the lowest, and the excess of Eu ([Eu/Fe]) is the highest, among the r-process-enhanced stars found so far. We consider possible scenarios to account for the detection of such a star and discuss techniques to enable searches for similar stars in the future. © 2010. The American Astronomical Society. All rights reserved.

Roche N.,University of Pennsylvania | Roche N.,National institute for astrophysics | Bernardi M.,University of Pennsylvania | Hyde J.,University of Pennsylvania
Monthly Notices of the Royal Astronomical Society | Year: 2010

We examine the colour-magnitude relation of ∼ 5000 brightest cluster galaxies (BCGs) in the Sloan Digital Sky Survey (SDSS). The colour-magnitude and colour-velocity dispersion relations of the BCGs are flatter in slope, by factors of 2 or more, than those of non-BCG early-type galaxies of similar luminosity (Mr < -22.5), while their g - r colours at the half-light radius are ∼ 0.01 mag redder.We investigate and compare radial colour gradients (which are usually negative) in these BCGs and a sample of 37 000 early-type galaxies, using a gradient estimator based on the ratio of de Vaucouleurs effective radii in g and r passbands, .reff(g)/reff(r) -1 The mean colour gradient of BCGs is flatter (by 23 per cent) than for other E/S0 galaxies of similar luminosity.The colour gradients in early-type galaxies are stronger at intermediate luminosity (Mr ≃ - 22) than at low or the highest luminosities, and tend to decrease with increasing velocity dispersion (σ). In non-BCG E/S0s, colour gradients increase for larger effective radii (up to 10-12 kpc), and are negatively correlated with 10 log σ + Mr, the mass density and stellar age. However, gradients can be reduced or inverted (positive) for post-starburst galaxies at the youngest ages. In BCGs, these trends are absent and the mean colour gradient remains at a relatively low level (∼ 0.08 by our measure) whatever the other properties of the galaxies. The redder half-light radius colours of the BCGs can be explained by their slightly greater ages combined with flatter radial colour gradients.We discuss possible explanations in terms of spheroidal galaxies initially having a colour gradient positively correlated with luminosity and positively correlated with large radius and/or low density. Subsequently, elliptical-elliptical 'dry' mergers progressively reduce colour gradients, towards a low but non-zero value. This has occurred a greater number of times during the formation histories of the most massive E/S0s, and to by far the greatest degree in the BCGs. © 2010 The Authors. Journal compilation © 2010 RAS.

Caprioli D.,National institute for astrophysics | Kang H.,Pusan National University | Vladimirov A.E.,Stanford University | Jones T.W.,University of Minnesota
Monthly Notices of the Royal Astronomical Society | Year: 2010

We provide a both qualitative and quantitative comparisons among different approaches aimed at solving the problem of non-linear diffusive acceleration of particles at shocks. In particular, we show that state-of-the-art models (numerical, Monte Carlo and semi-analytical), even if based on different physical assumptions and implementations, for typical environmental parameters lead to very consistent results in terms of shock hydrodynamics, cosmic ray spectrum and also escaping flux spectrum and anisotropy. Strong points and limits of each approach are also discussed, as a function of the problem one wants to study. © 2010 The Authors. Journal compilation © 2010 RAS.

Drake J.J.,Harvard - Smithsonian Center for Astrophysics | Orlando S.,National institute for astrophysics
Astrophysical Journal Letters | Year: 2010

Three-dimensional hydrodynamic simulations exploring the first 18 hr of the 2010 January 28 outburst of the recurrent nova U Scorpii have been performed. Special emphasis was placed on capturing the enormous range in spatial scales in the blast. The pre-explosion system conditions included the secondary star and a flared accretion disk. These conditions can have a profound influence on the evolving blast wave. The blast itself is shadowed by the secondary star, which itself gives rise to a low-temperature bow shock. The accretion disk is completely destroyed in the explosion. A model with a disk gas density of 1015 cm-3 produced a blast wave that is collimated and with clear bipolar structures, including a bipolar X-ray emitting shell. The degree of collimation depends on the initial mass of ejecta, energy of explosion, and circumstellar gas density distribution. It is most pronounced for a model with the lowest explosion energy (1043 erg) and mass of ejecta (10-8M⊙). The X-ray luminosities of three of six models computed are close to, but consistent with, an upper limit to the early blast X-ray emission obtained by the Swift satellite, the X-ray luminosity being larger for higher circumstellar gas density and higher ejecta mass. The latter consideration, together with estimates of the blast energy from previous outbursts, suggests that the mass of ejecta in the 2010 outburst was not larger than 10-7M⊙. © 2010. The American Astronomical Society.All rights reserved.

Risaliti G.,National institute for astrophysics | Risaliti G.,Harvard - Smithsonian Center for Astrophysics | Imanishi M.,Japan National Astronomical Observatory | Sani E.,University of Florence
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present a quantitative estimate of the relative active galactic nucleus (AGN)/starburst content in a sample of 59 nearby (z < 0.15) infrared bright ultraluminous infrared galaxies (ULIRGs) taken from the 1-Jy sample, based on infrared L-band (3-4 μm) spectra. By using diagnostic diagrams and a simple deconvolution model, we show that at least 60 per cent of local ULIRGs contain an active nucleus, but the AGN contribution to the bolometric luminosity is relevant only in ∼15-20 per cent of the sources. Overall, ULIRGs appear to be powered by the starburst process, responsible for >85 per cent of the observed infrared luminosity. The subsample of sources optically classified as low-ionization nuclear emission-line regions (LINERs; 31 objects) shows a similar AGN/starburst distribution as the whole sample, indicating a composite nature for this class of objects. We also show that a few ULIRGs, optically classified as starbursts, have L-band spectral features suggesting the presence of a buried AGN. © 2009 RAS.

Riva M.,National institute for astrophysics
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Wind is a well known performance detractor for telescope pointing. Increasing the size of the telescope increase the aeroelastic effect onto the performances of the telescope. A dome is often used for larger telescopes to minimize those interactions. Rapid pointing telescope requires rapid domes, which usually are heavy drawing their cost not negligible respect to the overall amount of budget required. For this reason fast telescope's dome are usually fully deployed leaving the telescope unprotected from the wind. This paper wants to show a modification of the fully foldable tents in order to realize a partially foldable light-weighted tent able to follow the alt-az fast movement of a large scale telescope protecting it from aeroelastic loading without interacting with the dynamic of the main system. The alt-az movement of the telescope is decoupled from an azimuth rotation of the full tent and an alt motion of the two shells. In this way it is possible to work with a fully emyspherical tent and aan opened window for the observations. © 2010 SPIE.

Persic M.,National institute for astrophysics | Rephaeli Y.,Tel Aviv University | Rephaeli Y.,University of California at San Diego
Monthly Notices of the Royal Astronomical Society | Year: 2010

Cosmic-ray energy densities in central regions of starburst galaxies, as inferred from radio and γ-ray measurements of, respectively, non-thermal synchrotron and π0-decay emission, are typically , i.e. typically at least an order of magnitude larger than near the Galactic Centre and in other not-very-actively star-forming galaxies. We first show that these very different energy density levels reflect a similar disparity in the respective supernova (SN) rates in the two environments, which is not unexpected given the SN origin of (Galactic) energetic particles. As a consequence of this correspondence, we then demonstrate that there is partial quantitative evidence that the stellar initial mass function (IMF) in starburst nuclei has a low-mass truncation at ∼2 M⊙, as predicted by theoretical models of turbulent media, in contrast with the much smaller value of 0.1 M⊙ that characterizes the low-mass cut-off of the stellar IMF in 'normal' galactic environments. © 2010 The Authors. Journal compilation © 2010 RAS.

Zamfir S.,University of Alabama | Sulentic J.W.,University of Alabama | Sulentic J.W.,Institute Astrofisica Of Andalucia | Marziani P.,National institute for astrophysics | Dultzin D.,National Autonomous University of Mexico
Monthly Notices of the Royal Astronomical Society | Year: 2010

We explore the properties of the Hβ emission line profile in a large, homogeneous and bright sample of N ∼ 470 low-redshift quasars extracted from Sloan Digital Sky Survey (Data Release 5). We approach the investigation from two complementary directions: composite/median spectra and a set of line diagnostic measures (asymmetry index, centroid shift and kurtosis) in individual quasars. The project is developed and presented in the framework of the so-called 4D Eigenvector 1 (4DE1) parameter space, with a focus on its optical dimensions, full width at half-maximum of broad Hβ[FWHM(Hβ)] and the relative strength of optical Fe ii[RFe ii≡ W(Fe ii4434-4684 Å)/W(Hβ)]. We reenforce the conclusion that not all quasars are alike and spectroscopically they do not distribute randomly about an average typical optical spectrum. Our results give further support to the concept of two populations A and B [narrower and broader than 4000 km s-1 FWHM(Hβ), respectively] that emerged in the context of 4DE1 space. The broad Hβ profiles in composite spectra of Population A sources are best described by a Lorentzian and in Population B by a double Gaussian model. Moreover, high- and low-accretion sources (an alternative view of the Population A/B concept) not only show significant differences in terms of black hole (BH) and Eddington ratio Lbol/LEdd, but they also show distinct properties in terms of line asymmetry, shift and shapes. We finally suggest that a potential refinement of the 4DE1 space can be provided by separating two populations of quasars at RFe ii∼ 0.50 rather than at FWHM(Hβ) = 4000 km s-1. Concomitantly, the asymmetry and centroid shift profile measures at 1/4 fractional intensity can be reasonable surrogates for the FWHM(Hβ) dimension of the current 4DE1. © 2010 The Authors. Journal compilation © 2010 RAS.

Frau P.,Institute Of Ciencies Of Lespai Csic Ieec | Girart J.M.,Institute Of Ciencies Of Lespai Csic Ieec | Beltran M.T.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2012

We use the new IRAM 30-m FTS backend to perform an unbiased ∼15 GHz wide survey at 3 mm toward the Pipe nebula young diffuse starless cores. We discover an unexpectedly rich chemistry. We propose a new observational classification based on the 3 mm molecular line emission normalized by the core visual extinction (A V). On the basis of this classification, we report a clear differentiation between cores in terms of chemical composition and line emission properties, which enables us to define three molecular core groups. The "diffuse" cores, A V ≈ 15, have a poor chemistry with mainly simple species (e.g. CS and C 2H). The "oxo-sulfurated" cores, A V ≈ 15-22, appear to be abundant in species such as SO and SO 2, but also in HCO, which seem to disappear at higher densities. Finally, the "deuterated" cores, A V ≈ 22, have a typical evolved chemistry prior to the onset of the star formation process, with nitrogenated and deuterated species, as well as carbon chain molecules. On the basis of these categories, one of the "diffuse" cores (core 47) has the spectral line properties of the "oxo-sulfurated" ones, which suggests that it is a failed core. © 2012 ESO.

Abramson L.E.,University of Chicago | Abramson L.E.,Carnegie Institution for Science | Kelson D.D.,Carnegie Institution for Science | Dressler A.,Carnegie Institution for Science | And 4 more authors.
Astrophysical Journal Letters | Year: 2014

The slope of the star formation rate/stellar mass relation (the SFR "Main Sequence"; SFR-M *) is not quite unity: specific star formation rates (SFR/M *) are weakly but significantly anti-correlated with M *. Here we demonstrate that this trend may simply reflect the well-known increase in bulge mass-fractions - portions of a galaxy not forming stars - with M *. Using a large set of bulge/disk decompositions and SFR estimates derived from the Sloan Digital Sky Survey, we show that re-normalizing SFR by disk stellar mass (sSFR disk ≡ SFR/M *, disk) reduces the M * dependence of SF efficiency by 0.25 dex per dex, erasing it entirely in some subsamples. Quantitatively, we find log sSFR disk-log M * to have a slope β disk ∈ [-0.20, 0.00] ± 0.02 (depending on the SFR estimator and Main Sequence definition) for star-forming galaxies with M * ≥ 1010 M ⊙ and bulge mass-fractions B/T ≲ 0.6, generally consistent with a pure-disk control sample (β control = -0.05 ± 0.04). That 〈SFR/M *, disk〉 is (largely) independent of host mass for star-forming disks has strong implications for aspects of galaxy evolution inferred from any SFR-M * relation, including manifestations of "mass quenching" (bulge growth), factors shaping the star-forming stellar mass function (uniform dlog M */dt for low-mass, disk-dominated galaxies), and diversity in star formation histories (dispersion in SFR(M *, t)). Our results emphasize the need to treat galaxies as composite systems - not integrated masses - in observational and theoretical work. © 2014. The American Astronomical Society. All rights reserved..

Smart R.L.,National institute for astrophysics
Astronomy and Computing | Year: 2016

We describe the Attitude Star Catalog produced for the Gaia mission. This catalog is being used by Gaia for the first on-ground attitude reconstruction. Originally it was simply a subset of the Initial Gaia Source List but this subset did not meet the isolation requirements and it contained a significant number of double entries. As a result during the commissioning phase of Gaia a new generation of this catalog, that better fulfills the attitude reconstruction requirements, was requested. Here we describe the production and properties of this new Attitude Star Catalog. The Attitude Star Catalog was made by combining 7 all sky catalogs and selecting entries based on magnitude, isolation and astrometric precision criteria. The catalog has 8173331 entries with estimates of the positions at 2000, proper motions and magnitudes (Gaia G, Gaia Grvs, red RF & blue BJ) in the magnitude range 7.0

Costigan G.,Dublin Institute for Advanced Studies | Costigan G.,College Hill | Costigan G.,European Southern Observatory | Scholz A.,Dublin Institute for Advanced Studies | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present the results of a variability study of accreting young stellar objects in the ChameleonI star-forming region, based on ∼300 high-resolution optical spectra from the Fibre Large Area Multi-Element Spectrograph (FLAMES) at the European Southern Observatory (ESO) Very Large Telescope (VLT). 25 objects with spectral types from G2-M5.75 were observed 12 times over the course of 15months. Using the emission lines Hα (6562.81Å) and Caii (8662.1Å) as accretion indicators, we found 10 accreting and 15 non-accreting objects. We derived accretion rates for all accretors in the sample using the Hα equivalent width, Hα 10 per cent width and Caii (8662.1Å) equivalent width. We found that the Hα equivalent widths of accretors varied by ∼7-100Å over the 15-month period. This corresponds to a mean amplitude of variations in the derived accretion rate of ∼0.37dex. The amplitudes of variations in the derived accretion rate from Caii equivalent width were ∼0.83dex and those from Hα 10 per cent width were ∼1.11dex. Based on the large amplitudes of variations in accretion rate derived from the Hα 10 per cent width with respect to the other diagnostics, we do not consider it to be a reliable accretion rate estimator. Assuming the variations in Hα and Caii equivalent width accretion rates to be closer to the true value, these suggest that the spread that was found around the accretion rate to stellar-mass relation is not due to the variability of individual objects on time-scales of weeks to ∼1year. From these variations, we can also infer that the accretion rates are stable within <0.37dex over time-scales of less than 15months. A major portion of the accretion variability was found to occur over periods shorter than the shortest time-scales in our observations, 8-25days, which are comparable with the rotation periods of these young stellar objects. This could be an indication that what we are probing is spatial structure in the accretion flows and it also suggests that observations on time-scales of ∼a couple of weeks are sufficient to limit the total extent of accretion-rate variations in typical young stars. No episodic accretion was observed: all 10 accretors accreted continuously for the entire period of observations and, though they may have undetected low accretion rates, the non-accretors never showed any large changes in their emission that would imply a jump in accretion rate. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Gibbons P.G.,Institute for Astronomy | Rice W.K.M.,Institute for Astronomy | Mamatsashvili G.R.,National institute for astrophysics | Mamatsashvili G.R.,Tbilisi State University
Monthly Notices of the Royal Astronomical Society | Year: 2012

We study particle dynamics in local two-dimensional simulations of self-gravitating accretion discs with a simple cooling law. It is well known that the structure which arises in the gaseous component of the disc due to a gravitational instability can have a significant effect on the evolution of dust particles. Previous results using global simulations indicate that spiral density waves are highly efficient at collecting dust particles, creating significant local overdensities which may be able to undergo gravitational collapse. We expand on these findings using a range of cooling times to mimic the conditions at a large range of radii within the disc. Here we use the pencil code to solve the 2D local shearing sheet equations for gas on a fixed grid together with the equations of motion for solids coupled to the gas solely through aerodynamic drag force. We find that spiral density waves can create significant enhancements in the surface density of solids, equivalent to 1-10cm sized particles in a disc following the profiles of Clarke around an ∼1M ⊙ star, causing it to reach concentrations several orders of magnitude larger than the particles mean surface density. We also study the velocity dispersion of the particles, finding that the spiral structure can result in the particle velocities becoming highly ordered, having a narrow velocity dispersion. This implies low relative velocities between particles, which in turn suggest that collisions are typically low energy, lessening the likelihood of grain destruction. Both these findings suggest that the density waves that arise due to gravitational instabilities in the early stages of star formation provide excellent sites for the formation of large, planetesimal-sized objects. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Bucciantini N.,National institute for astrophysics | Bucciantini N.,National Institute of Nuclear Physics, Italy
Astronomische Nachrichten | Year: 2014

Pulsar-wind nebulae (PWNe) are ideal astro-physical laboratories where high energy relativistic phenomena can be inves-tigated. They are close, well resolved in our observations, and the knowledge derived in their study has a strong impact in many other fields, from AGNs to GRBs. Yet there are still unresolved issues, that prevent us from a full clear under-standing of these objects. The lucky combination of high resolution X-ray imaging and numerical codes to handle the outflow and dynamical properties of relativistic MHD, has opened a new avenue of investigation that has lead to inter-esting progressed in the last years. Despite all of these, we do not understand yet how particles are accelerated, and the functioning of the pulsar wind and pulsar magnetosphere, that power PWNe. I will review what is now commonly known as the MHD paradigm, and in particular I will focus on various approaches that have been and are currently used to model these systems. For each I will highlight its advantages and limitations, and degree of applicability. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Salmi F.,University Paris Diderot | Daddi E.,University Paris Diderot | Elbaz D.,University Paris Diderot | Sargent M.T.,University Paris Diderot | And 4 more authors.
Astrophysical Journal Letters | Year: 2012

Using a mass-limited sample of 24 μm detected, star-forming galaxies at 0.5 < z < 1.3, we study the mass-star formation rate (SFR) correlation and its tightness. The correlation is well defined (σ = 0.28dex) for disk galaxies (n Sérsic < 1.5), while more bulge-dominated objects often have lower specific SFRs (sSFRs). For disk galaxies, a much tighter correlation (σ = 0.19dex) is obtained if the rest-frame H-band luminosity is used instead of stellar mass derived from multi-color photometry. The sSFR correlates strongly with rest-frame optical colors (hence luminosity-weighted stellar age) and also with clumpiness (which likely reflects the molecular gas fraction). This implies that most of the observed scatter is real, despite its low level, and not dominated by random measurement errors. After correcting for these differential effects a remarkably small dispersion remains (σ = 0.14dex), suggesting that measurement errors in mass or SFR are ≲ 0.10dex, excluding systematic uncertainties. Measurement errors in stellar masses, the thickening of the correlation due to real sSFR variations, and varying completeness with stellar mass, can spuriously bias the derived slope to lower values due to the finite range over which observables (mass and SFR) are available. When accounting for these effects, the intrinsic slope for the main sequence for disk galaxies gets closer to unity. © 2012. The American Astronomical Society. All rights reserved.

Marziani P.,National institute for astrophysics | Sulentic J.W.,Institute Astrofisica Of Andalucia
New Astronomy Reviews | Year: 2012

We review past work using broad emission lines as virial estimators of black hole masses in quasars. Basically one requires estimates of the emitting region radius and virial velocity dispersion to obtain black hole masses. The three major ways to estimate the broad-line emitting region (BLR) radius involve: (1) direct reverberation mapping, (2) derivation of BLR radius for larger samples using the radius-luminosity correlation derived from reverberation measures, and (3) estimates of BLR radius using the definition of the ionization parameter solved for BLR radius (photoionization method). At low redshift (z≲0.7) FWHM Hβ serves as the most widely used estimator of virial velocity dispersion. FWHM Hβ can provide estimates for tens of thousands of quasars out to z≈3.8 (IR spectroscopy beyond z≈1). A new photoionization method also shows promise for providing many reasonable estimates of BLR radius via high S/N IR spectroscopy of the UV region 1300-2000Å. FWHM Mgiiλ2800 can serve as a surrogate for FWHM Hβ in the range 0.4≲z≲6.5 while civλ1549 is affected by broadening due to non-virial motions and best avoided (i.e. there is no clear conversion factor between FWHM Hβ and FWHM Civλ1549). Most quasars yield mass estimates in the range 7≲log M BH≲9.7. There is no strong evidence for values above 10.0 and there may be evidence for a turnover in the maximum black hole mass near z≈5. © 2011 Elsevier B.V.

Villata M.,National institute for astrophysics
Astrophysics and Space Science | Year: 2012

In this short paper we reply to the Comment by M. J. T. F. Cabbolet on Villata's theory of antigravity. The criticisms of methodological and ontological kind presented by that author come from a misinterpretation of some concepts, perhaps due to some lack of clarity or omission of details in Villata's original article. In order to clarify these points, here we provide additional explanations regarding the assumptions and results of the theory. © 2011 Springer Science+Business Media B.V.

Jones B.M.,University of Hawaii at Manoa | Kaiser R.I.,University of Hawaii at Manoa | Strazzulla G.,National institute for astrophysics
Astrophysical Journal | Year: 2014

Ozone has been detected on the surface of Ganymede via observation of the Hartley band through the use of ultraviolet spectroscopy and is largely agreed upon to be formed by radiolytic processing via interaction of magnetospheric energetic ions and/or electrons with oxygen-bearing ices on Ganymede's surface. Interestingly, a clearly distinct band near 300 nm within the shoulder of the UV-Vis spectrum of Ganymede was also observed, but currently lacks an acceptable physical or chemical explanation. Consequently, the primary motivation behind this work was the collection of UV-Vis absorption spectroscopy of ozone formation by energetic electron bombardment of a variety of oxygen-bearing ices (oxygen, carbon dioxide, water) relevant to this moon as well as other solar system. Ozone was indeed synthesized in pure ices of molecular oxygen, carbon dioxide and a mixture of water and oxygen, in agreement with previous studies. The Hartley band of the ozone synthesized in these ice mixtures was observed in the UV-Vis spectra and compared with the spectrum of Ganymede. In addition, a solid state ozone absorption cross section of 6.0 ± 0.6 × 10 -17 cm2 molecule-1 was obtained from the UV-Vis spectral data. Ozone was not produced in the irradiated carbon dioxide-water mixtures; however, a spectrally "red" UV continuum is observed and appears to reproduce well what is observed in a large number of icy moons such as Europa. © 2014. The American Astronomical Society. All rights reserved.

Koumpia E.,SRON Netherlands Institute for Space Research | Bonanos A.Z.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2012

Context. Only a small number of high mass stars (>30 M ·) have fundamental parameters (i.e. masses and radii) measured with high enough accuracy from eclipsing binaries to constrain formation and evolutionary models of massive stars. Aims. This work aims to increase this limited sample, by studying the four massive eclipsing binary candidates discovered by Bonanos in the young massive cluster Westerlund 1. Methods. We present new follow-up echelle spectroscopy of these binaries and models of their light and radial velocity curves. Results. We obtain fundamental parameters for the eight component stars, finding masses that span a range of 10-40 M ·, and contributing accurate fundamental parameters for one additional very massive star, the 33 M · component of W13. WR77o is found to have a ∼40 M · companion, which provides a second dynamical constraint on the mass of the progenitor of the magnetar known in the cluster. We also use W13 to estimate the first, direct, eclipsing binary distance to Westerlund 1 and therefore the magnetar and find it to be at 3.7 ± 0.6 kpc. Conclusions. Our results confirm previous evidence for a high mass for the progenitor of the magnetar. In addition, the availability of eclipsing binaries with accurate parameters opens the way for direct, independent, high precision eclipsing binary distance measurements to Westerlund 1. © 2012 ESO.

Redlich M.,University of Heidelberg | Bartelmann M.,University of Heidelberg | Waizmann J.-C.,University of Bologna | Waizmann J.-C.,National institute for astrophysics | And 2 more authors.
Astronomy and Astrophysics | Year: 2012

For more than a decade now, it has been controversial whether or not the high rate of giant gravitational arcs and the largest observed Einstein radii are consistent with the standard cosmological model. Recent studies indicate that mergers provide an efficient mechanism to substantially increase the strong-lensing efficiency of individual clusters. Based on purely semi-analytic methods, we investigated the statistical impact of cluster mergers on the distribution of the largest Einstein radii and the optical depth for giant gravitational arcs of selected cluster samples. Analysing representative all-sky realizations of clusters at redshifts z < 1 and assuming a constant source redshift of zs = 2:0, we find that mergers increase the number of Einstein radii above 10′′ (20′′) by ∼35% (∼55%). Exploiting the tight correlation between Einstein radii and lensing cross sections, we infer that the optical depth for giant gravitational arcs with a length-to-width ratio ≥7:5 of those clusters with Einstein radii above 10′′ (20′′) increases by ∼45% (∼85%). Our findings suggest that cluster mergers significantly influence in particular the statistical lensing properties of the strongest gravitational lenses. We conclude that semi-analytic studies must inevitably take these events into account before questioning the standard cosmological model on the basis of the largest observed Einstein radii and the statistics of giant gravitational arcs. © 2012 ESO.

Reynolds S.P.,North Carolina State University | Gaensler B.M.,University of Sydney | Bocchino F.,National institute for astrophysics
Space Science Reviews | Year: 2012

We review the observations of supernova remnants (SNRs) and pulsar-wind nebulae (PWNe) that give information on the strength and orientation of magnetic fields. Radio polarimetry gives the degree of order of magnetic fields, and the orientation of the ordered component. Many young shell supernova remnants show evidence for synchrotron X-ray emission. The spatial analysis of this emission suggests that magnetic fields are amplified by one to two orders of magnitude in strong shocks. Detection of several remnants in TeV gamma rays implies a lower limit on the magnetic-field strength (or a measurement, if the emission process is inverse-Compton upscattering of cosmic microwave background photons). Upper limits to GeV emission similarly provide lower limits on magnetic-field strengths. In the historical shell remnants, lower limits on B range from 25 to 1000 ?G. Two remnants show variability of synchrotron X-ray emission with a timescale of years. If this timescale is the electron-acceleration or radiative loss timescale, magnetic fields of order 1 mG are also implied. In pulsar-wind nebulae, equipartition arguments and dynamical modeling can be used to infer magnetic-field strengths anywhere from ∼ μG to 1 mG. Polarized fractions are considerably higher than in SNRs, ranging to 50 or 60% in some cases; magnetic-field geometries often suggest a toroidal structure around the pulsar, but this is not universal. Viewing-angle effects undoubtedly play a role. MHD models of radio emission in shell SNRs show that different orientations of upstream magnetic field, and different assumptions about electron acceleration, predict different radio morphology. In the remnant of SN 1006, such comparisons imply a magnetic-field orientation connecting the bright limbs, with a substantial density gradient across the remnant. © 2011 Springer Science+Business Media B.V.

Waizmann J.-C.,University of Bologna | Waizmann J.-C.,National institute for astrophysics | Waizmann J.-C.,National Institute of Nuclear Physics, Italy | Redlich M.,University of Heidelberg | Bartelmann M.,University of Heidelberg
Astronomy and Astrophysics | Year: 2012

Context. With the amount and quality of galaxy cluster data increasing, the question arises whether or not the standard cosmological model can be questioned on the basis of a single observed extreme galaxy cluster. Usually, the word extreme refers directly to cluster mass, which is not a direct observable and thus subject to substantial uncertainty. Hence, it is desirable to extend studies of extreme clusters to direct observables, such as the Einstein radius. Aims. We aim to evaluate the occurrence probability of the large observed Einstein radius of MACS J0717.5+3745 within the standard ΛCDM cosmology. In particular, we want to model the distribution function of the single largest Einstein radius in a given cosmological volume and to study which underlying assumptions and effects have the strongest impact on the results. Methods. We obtain this distribution by a Monte Carlo approach, based on the semi-analytic modelling of the halo population on the past lightcone. After sampling the distribution, we fit the results with the general extreme value (GEV) distribution which we use for the subsequent analysis. Results. We find that the distribution of the maximum Einstein radius is particularly sensitive to the precise choice of the halo mass function, lens triaxiality, the inner slope of the halo density profile and the mass-concentration relation. Using the distributions so obtained, we study the occurrence probability of the large Einstein radius of MACS J0717.5+3745, finding that this system is not in tension with ΛCDM. We also find that the GEV distribution can be used to fit very accurately the sampled distributions and that all of them can be described by a (type-II) Fréchet distribution. Conclusions. With a multitude of effects that strongly influence the distribution of the single largest Einstein radius, it is more than doubtful that the standard ΛCDM cosmology can be ruled out on the basis of a single observation. If, despite the large uncertainties in the underlying assumptions, one wanted to do so, a much larger Einstein radius (≳ 100″) than that of MACS J0717.5+3745 would have to be observed. © 2012 ESO.

Vernetto S.,National institute for astrophysics
Astrophysics and Space Sciences Transactions | Year: 2011

In this paper we report on the observations of TeV gamma ray sources performed by the air shower detector ARGO-YBJ. The objects studied in this work are the blazar Markarian 421 and the extended galactic source MGROJ1908+06, monitored during ∼2 years of operation. Mrk421 has been detected by ARGO-YBJ with a statistical significance of ∼11 standard deviations. The observed TeV emission was highly variable, showing large enhancements of the flux during active periods. The study of the spectral behaviour during flares revealed a positive correlation of the hardness with the flux, as already reported in the past by the Whipple telescope, suggesting that this is a long term property of the source. ARGO-YBJ observed a strong correlation between TeV gamma rays and the X-ray flux measured by RXTM/ASM and SWIFT/BAT during the whole period, with a time lag compatible with zero, supporting the one-zone SSC model to describe the emission mechanism. MGROJ1908+06 has been detected by ARGO-YBJ with ∼5 standard deviation of significance. From our data the source appears extended and the measured extension is σ ext=0.48° -0.28 +0.26, in agreement with a previous HESS observation. The average flux is in marginal agreement with that reported by MILAGRO, but significantly higher than that obtained by HESS, suggesting a possible flux variability. The large field of view (∼2 sr) and the high duty cycle allow a continuous monitoring of the sky in the declination band from -0° to 70°. In this paper we report on the observations of two bright gamma ray sources, performed during ∼2 years: the blazar Mrk421 and the extended galactic source MGROJ1908+06. © Author(s) 2011.

Hook I.M.,University of Oxford | Hook I.M.,National institute for astrophysics
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2013

Prospects for future supernova surveys are discussed, focusing on the European Space Agency's Euclid mission and the European Extremely Large Telescope (E-ELT), both expected to be in operation around the turn of the decade. Euclid is a 1.2m space survey telescope that will operate at visible and near-infrared wavelengths, and has the potential to find and obtain multi-band lightcurves for thousands of distant supernovae. The E-ELT is a planned, general-purpose ground-based, 40-mclass optical-infrared telescope with adaptive optics built in, which will be capable of obtaining spectra of type Ia supernovae to redshifts of at least four. The contribution to supernova cosmology with these facilities will be discussed in the context of other future supernova programmes such as those proposed for DES, JWST, LSST and WFIRST. © 2013 The Author(s) Published by the Royal Society. All rights reserved.

Brunetti G.,National institute for astrophysics
Plasma Physics and Controlled Fusion | Year: 2015

Acceleration of cosmic-ray electrons (CRe) in the intra-cluster medium (ICM) is probed by radio observations that detect diffuse, megaparsec-scale, synchrotron sources in a fraction of galaxy clusters. Giant radio halos are the most spectacular manifestations of non-thermal activity in the ICM and are currently explained assuming that turbulence, driven during massive cluster-cluster mergers, reaccelerates CRe at several giga-electron volts. This scenario implies a hierarchy of complex mechanisms in the ICM that drain energy from large scales into electromagnetic fluctuations in the plasma and collisionless mechanisms of particle acceleration at much smaller scales. In this paper we focus on the physics of acceleration by compressible turbulence. The spectrum and damping mechanisms of the electromagnetic fluctuations, and the mean free path (mfp) of CRe, are the most relevant ingredients that determine the efficiency of acceleration. These ingredients in the ICM are, however, poorly known, and we show that calculations of turbulent acceleration are also sensitive to these uncertainties. On the other hand this fact implies that the non-thermal properties of galaxy clusters probe the complex microphysics and the weakly collisional nature of the ICM. © 2016 IOP Publishing Ltd.

Papadopoulos P.P.,Max Planck Institute for Radio Astronomy | van der Werf P.P.,Leiden University | van der Werf P.P.,University of Edinburgh | Xilouris E.M.,National institute for astrophysics | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We report results from a large molecular line survey of luminous infrared galaxies (LIRGs; L IR ≳1011L) in the local Universe (z ≤ 0.1), conducted during the last decade with the James Clerk Maxwell Telescope and the IRAM 30-m telescope. This work presents the CO and 13CO line data for 36 galaxies, further augmented by multi-J total CO line luminosities available for other infrared (IR) bright galaxies from the literature. This yields a combined sample of N = 70 galaxies with the star formation (SF) powered fraction of their IR luminosities spanning L IR ∼(1010--2×1012)L and a wide range of morphologies. Simple comparisons of their available CO spectral line energy distributions (SLEDs) with local ones, as well as radiative transfer models, discern a surprisingly wide range of average interstellar medium (ISM) conditions, with most of the surprises found in the high-excitation regime. These take the form of global CO SLEDs dominated by a very warm (T kin ≳100K) and dense (n ≥ 10 4cm -3) gas phase, involving galaxy-sized (∼(few) × 10 9M ⊙) gas mass reservoirs under conditions that are typically found only for ∼(1-3) percent of mass per typical SF molecular cloud in the Galaxy. Furthermore, some of the highest excitation CO SLEDs are found in ultraluminous infrared galaxies (ULIRGs; L IR ≥ 10 12L ⊙) and surpass even those found solely in compact SF-powered hot spots in Galactic molecular clouds. Strong supersonic turbulence and high cosmic ray energy densities rather than far-ultraviolet/optical photons or supernova remnant induced shocks from individual SF sites can globally warm the large amounts of dense gas found in these merger-driven starbursts and easily power their extraordinary CO line excitation. This exciting possibility can now be systematically investigated with Herschel and the Atacama Large Milimeter Array (ALMA). As expected for an IR-selected (and thus SF rate selected) galaxy sample, only few 'cold' CO SLEDs are found, and for fewer still a cold low/moderate-density and gravitationally bound state (i.e. Galactic type) emerges as the most likely one. The rest remain compatible with a warm and gravitationally unbound low-density phase often found in ULIRGs. Such degeneracies, prominent when only the low-J SLED segment (J = 1-0, 2-1 and 3-2) is available, advise against using its CO line ratios and the so-called X co = M(H 2)/L co(1-0) factor as SF mode indicators, a practice that may have led to the misclassification of the ISM environments of IR-selected gas-rich discs in the distant Universe. Finally, we expect that the wide range of ISM conditions found among LIRGs will strongly impact the X co factor, an issue we examine in detail in Paper II. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Mucciarelli A.,University of Bologna | Dalessandro E.,University of Bologna | Ferraro F.R.,University of Bologna | Origlia L.,National institute for astrophysics | Lanzoni B.,University of Bologna
Astrophysical Journal Letters | Year: 2014

We have studied the chemical composition of NGC 1806, a massive, intermediate-age globular cluster that shows a double main sequence turnoff. We analyzed a sample of high-resolution spectra (secured with FLAMES at the Very Large Telescope) for eight giant stars, members of the cluster, finding an average iron content of [Fe/H]=-0.60 ± 0.01 dex and no evidence of intrinsic star-to-star variations in the abundances of light elements (Na, O, Mg, Al). Also, the (mF814W; mF336W - mF814W) color-magnitude diagram obtained by combining optical and near-UV Hubble Space Telescope photometry exhibits a narrow red giant branch, thus ruling out intrinsic variations of C and N abundances in the cluster. These findings demonstrate that NGC 1806 does not harbor chemically distinct sub-populations, at variance with what was found in old globular clusters. In turn, this indicates that the double main sequence turnoff phenomenon cannot be explained in the context of the self-enrichment processes usually invoked to explain the chemical anomalies observed in old globulars. Other solutions (i.e., stellar rotation, merging between clusters, or collisions with giant molecular clouds) should be envisaged to explain this class of globulars. © 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

Uttley P.,University of Amsterdam | Casella P.,National institute for astrophysics
Space Science Reviews | Year: 2014

Multiwavelength variability data, combined with spectral-timing analysis techniques, provides information about the causal relationship between different physical components in accreting black holes. Using fast-timing data and long-term monitoring, we can probe the behaviour of the same components across the black hole mass scale. In this chapter we review the observational status of multiwavelength variability in accreting black holes, from black hole X-ray binaries to AGN, and consider the implications for models of accretion and ejection, primarily considering the evidence for accretion disc and jet variability in these systems. We end with a consideration of future prospects in this quickly-developing field. © 2014, Springer Science+Business Media Dordrecht.

Mao J.,Korea Astronomy and Space Science Institute | Mao J.,National institute for astrophysics | Mao J.,Chinese Academy of Sciences | Wang J.,Chinese Academy of Sciences
Astrophysical Journal | Year: 2011

We revisit the radiation mechanism of relativistic electrons in the stochastic magnetic field and apply it to the high-energy emissions of gamma-ray bursts (GRBs). We confirm that jitter radiation is a possible explanation for GRB prompt emission in the condition of a large electron deflection angle. In the turbulent scenario, the radiative spectral property of GRB prompt emission is decided by the kinetic energy spectrum of turbulence. The intensity of the random and small-scale magnetic field is determined by the viscous scale of the turbulent eddy. The microphysical parameters εe and εB can be obtained. The acceleration and cooling timescales are estimated as well. Due to particle acceleration in magnetized filamentary turbulence, the maximum energy released from the relativistic electrons can reach a value of about 1014 eV. The GeV GRBs are possible sources of high-energy cosmic-ray. © 2011. The American Astronomical Society. All rights reserved.

Bonanno A.,National institute for astrophysics | Bonanno A.,National Institute of Nuclear Physics, Italy | Reuter M.,University of Mainz
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We discuss the stabilization of the conformal factor by higher derivative terms in a conformally reduced R+R2 Euclidean gravity theory. The flat spacetime is unstable towards the condensation of modes with nonzero momentum, and they "condense" in a modulated phase above a critical value of the coupling β of the R2 term. By employing a combination of variational, numerical and lattice methods, we show that in the semiclassical limit the corresponding functional integral is dominated by a single nonlinear plane wave of frequency ≈1/√βℓPl. We argue that the ground state of the theory is characterized by a spontaneous breaking of translational invariance at Planckian scales. © 2013 American Physical Society.

Cecchi-Pestellini C.,National institute for astrophysics | Duley W.W.,University of Waterloo | Williams D.A.,University College London
Astrophysical Journal | Year: 2012

Laboratory evidence suggests that recombination of adsorbed radicals may cause an abrupt temperature excursion of a dust grain to about 1000K. One consequence of this is the rapid desorption of adsorbed H2 molecules with excitation temperatures of this magnitude. We compute the consequences of injection of hot H2 into cold diffuse interstellar gas at a rate of 1% of the canonical H2 formation rate. We find that the level populations of H2 in J = 3, 4, and 5 are close to observed values, and that the abundances of CH+ and OH formed in reactions with hot hydrogen are close to the values obtained from observations of diffuse clouds. © © 2012. The American Astronomical Society. All rights reserved..

Tortora C.,University of Zurich | Napolitano N.R.,National institute for astrophysics | Romanowsky A.J.,University of California at Santa Cruz | Jetzer P.,University of Zurich
Astrophysical Journal Letters | Year: 2010

We analyze the correlations between central dark matter (DM) content of early-type galaxies and their sizes and ages, using a sample of intermediate-redshift (z ∼ 0.2) gravitational lenses from the SLACS survey, and by comparing them to a larger sample of z ∼ 0 galaxies. We decompose the deprojected galaxy masses into DM and stellar components using combinations of strong lensing, stellar dynamics, and stellar populations modeling. For a given stellar mass, we find that for galaxies with larger sizes, the DM fraction increases and the mean DM density decreases, consistently with the cuspy halos expected in cosmological formation scenarios. The DM fraction also decreases with stellar age, which can be partially explained by the inverse correlation between size and age. The residual trend may point to systematic dependencies on formation epoch of halo contraction or stellar initial mass functions. These results are in agreement with recent findings based on local galaxies by Napolitano et al. and suggest negligible evidence of galaxy evolution over the last ∼2.5 Gyr other than passive stellar aging. © 2010. The American Astronomical Society. All rights reserved.

Mason E.,US Space Telescope Science Institute | Williams R.E.,US Space Telescope Science Institute | Della Valle M.,National institute for astrophysics | Setiawan J.,Embassy of the Republic of Indonesia
Astronomy and Astrophysics | Year: 2012

We present optical and near-infrared (NIR) spectroscopic observations of U Sco 2010 outburst. From the analysis of lines profiles we identify a broad and a narrow component and show that the latter originates from the reforming accretion disk. We show that the accretion resumes shortly after the outburst, on day +8, roughly when the super-soft (SSS) X-ray phase starts. Consequently U Sco SSS phase is fueled (in part or fully) by accretion and should not be used to estimate m rem, the mass of accreted material which has not been ejected during the outburst. In addition, most of the He emission lines, and the He ii lies in particular, form in the accretion flow/disk within the binary and are optically thick, thus preventing an accurate abundance determination. A late spectrum taken in quiescence and during eclipse shows Ca ii H&K, the G-band and Mg ib absorption from the secondary star. However, no other significant secondary star features have been observed at longer wavelengths and in the NIR band. © 2012 ESO.

Andreon S.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2012

This work measures the evolution of the iron content in galaxy clusters by a rigorous analysis of the data of 130 clusters at 0.1 < z < 1.3. This task is made difficult by a) the low signal-to-noise ratio of abundance measurements and the upper limits; b) possible selection effects; c) boundaries in the parameter space; d) non-Gaussian errors; e) the intrinsic variety of the objects studied; and f) abundance systematics. We introduce a Bayesian model to address all these issues at the same time, thus allowing cross-talk (covariance). On simulated data, the Bayesian fit recovers the input enrichment history, unlike in standard analysis. After accounting for a possible dependence on X-ray temperature, for metal abundance systematics, and for the intrinsic variety of studied objects, we found that the present-day metal content is not reached either at high or at low redshifts, but gradually over time: iron abundance increases by a factor 1.5 in the 7 Gyr sampled by the data. Therefore, feedback in metal abundance does not end at high redshift. Evolution is established with a moderate amount of evidence, 19 to 1 odds against faster or slower metal enrichment histories. We quantify, for the first time, the intrinsic spread in metal abundance, 18 ± 3%, after correcting for the effect of evolution, X-ray temperature, and metal abundance systematics. Finally, we also present an analytic approximation of the X-ray temperature and metal abundance likelihood functions, which are useful for other regression fitting involving these parameters. The data for the 130 clusters and code used for the stochastic computation are provided with the paper. ©2012 ESO.

Sollima A.,National institute for astrophysics | Mastrobuono Battisti A.,Technion - Israel Institute of Technology
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present a new implementation of the Monte Carlo method to simulate the evolution of star clusters. The major improvement with respect to the previously developed codes is the treatment of the external tidal field taking into account for both the loss of stars from the cluster boundary and the disc/bulge shocks.We provide recipes to handle with eccentric orbits in complex galactic potentials. The first calculations for stellar systems containing 21 000 and 42 000 equal-mass particles show good agreement with direct N-body simulations in terms of the evolution of both the enclosed mass and the Lagrangian radii provided that the mass-loss rate does not exceed a critical value. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Cui W.,University of Western Australia | Cui W.,University of Trieste | Borgani S.,University of Trieste | Borgani S.,National institute for astrophysics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We investigate baryon effects on the halo mass function (HMF), with emphasis on the role played by active galactic nuclei (AGN) feedback. Haloes are identified with both friends-offriends (FoF) and spherical overdensity (SO) algorithms.We embed the standard SO algorithm into a memory-controlled frame program and present the Python spherIcAl Overdensity code-PIAO (Chinese character: ). For both FoF and SO haloes, the effect of AGN feedback is that of suppressing the HMFs to a level even below that of dark matter (DM) simulations. The ratio between the HMFs in the AGN and in the DM simulations is ∼0.8 at overdensity Δc = 500, a difference that increases at higher overdensity Δc = 2500, with no significant redshift and mass dependence. A decrease of the halo masses ratio with respect to the DM case induces the decrease of the HMF in the AGN simulation. The shallower inner density profiles of haloes in the AGN simulation witnesses that mass reduction is induced by the sudden displacement of gas induced by thermal AGN feedback. We provide fitting functions to describe halo mass variations at different overdensities, which can recover the HMFs with a residual random scatter ≲5 per cent for halo masses larger than 1013 h-1M⊙. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Salvaterra R.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Haardt F.,University of Insubria | Haardt F.,National Institute of Nuclear Physics, Italy | Volonteri M.,IAP | Moretti A.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2012

We place firm upper limits on the global accretion history of massive black holes at z > 5 from the recently measured unresolved fraction of the cosmic X-ray background. The maximum allowed unresolved intensity observed at 1.5 keV implies a maximum accreted-mass density onto massive black holes of ρ acc < 1.4 × 10 4 M Mpc -3 for z > 5. Considering the contribution of lower-z AGNs, the value reduces to ρ acc < 0.66 × 10 4 MMpc -3. The tension between the need for the efficient and rapid accretion required by the observation of massive black holes already in place at z > 7 and the strict upper limit on the accreted mass derived from the X-ray background may indicate that black holes are rare in high redshift galaxies or that accretion is only efficient for the black holes hosted by rare galaxies. © 2012 ESO.

Battaglia G.,Hemisphere | Battaglia G.,National institute for astrophysics | Starkenburg E.,University of Groningen
Astronomy and Astrophysics | Year: 2012

Dwarf galaxies provide insight into the processes of star formation and chemical enrichment at the low end of the galaxy mass function, as well as into the clustering of dark matter on small scales. In studies of Local Group dwarf galaxies, spectroscopic samples of individual stars are used to derive the internal kinematics and abundance properties of these galaxies. It is therefore important to clean these samples from Milky Way stars, which are not related to the dwarf galaxy, since they can contaminate analysis of the properties of these objects. Here we introduce a new diagnostic for separating Milky Way contaminant stars, which mainly consist of dwarf stars, and red giant branch stars targeted in dwarf galaxies. As discriminator we use the trends in the equivalent width of the nIR Mg I line at 8806.8 Å as a function of the equivalent width of Ca II triplet lines. This method is particularly useful for works dealing with multi-object, intermediate-resolution spectroscopy focusing in the region of the nIR Ca II triplet. We use synthetic spectra to explore how the equivalent width of these lines changes for stars with different properties (gravity, effective temperature, metallicity) and find that a distinction among giants above the horizontal branch and dwarfs can be made with this method at [Fe/H] > -2 dex. For -2 ≤ [Fe/H] ≤ -1, this method is also valid for distinguishing dwarfs and giants down to approximately one magnitude below the horizontal branch. Using a foreground model we make predictions on the use of this new discrimination method for nearby dwarf spheroidal galaxies, including the ultra-faints. We subsequently use VLT/FLAMES data for the Sextans, Sculptor, and Fornax dwarf spheroidal galaxies to verify the predicted theoretical trends. © ESO 2012.

Vazza F.,Jacobs University Bremen | Vazza F.,National institute for astrophysics | Roediger E.,Jacobs University Bremen | Bruggen M.,Jacobs University Bremen
Astronomy and Astrophysics | Year: 2012

We have designed a simple multi-scale method that identifies turbulent motions in hydrodynamical grid simulations. The method does not assume any a priori coherence scale to distinguish laminar and turbulent flows. Instead, the local mean velocity field around each cell is reconstructed with a multi-scale filtering technique, yielding the maximum scale of turbulent eddies by means of iterations. The method is robust, fast, and easily applicable to any grid simulation. We present here the application of this technique to the study of spatial and spectral properties of turbulence in the intra-cluster medium, measuring turbulent diffusion and anisotropy of the turbulent velocity field for a variety of driving mechanisms: a) accretion of matter in galaxy clusters (simulated with ENZO); b) sloshing motions around cool-cores (simulated with FLASH); c) jet outflows from active galactic nuclei (AGN, simulated with FLASH). The turbulent velocities driven by matter accretion in galaxy clusters are mostly tangential in the inner regions (inside the cluster virial radius) and isotropic in regions close to the virial radius. The same is found for turbulence excited by cool-core sloshing, while the jet outflowing from AGN drives mostly radial turbulence motions near its sonic point and beyond. Turbulence leads to a diffusivity in the range Dturb ∼ 10 29-1030 cm2 s-1 in the intra-cluster medium. On average, the energetically dominant mechanism of turbulence driving in the intra cluster medium is represented by accretion of matter and major mergers during cluster evolution. © ESO 2012.

Blasi P.,National institute for astrophysics | Blasi P.,National Institute of Nuclear Physics, Italy
Nuclear Physics B - Proceedings Supplements | Year: 2014

The search for a theory of the origin of cosmic rays that may be considered as a standard, agreeable model is still ongoing. On one hand, much circumstantial evidence exists of the fact that supernovae in our Galaxy play a crucial role in producing the bulk of cosmic rays observed on Earth. On the other hand, important questions about their ability to accelerate particles up to the knee remain unanswered. The common interpretation of the knee as a feature coinciding with the maximum energy of the light component of cosmic rays and a transition to a gradually heavier mass composition is mainly based on KASCADE results. Some recent data appear to question this finding: YAC1-Tibet Array and ARGO-YBJ find a flux reduction in the light component at ~ 700 TeV, appreciably below the knee. Whether the maximum energy of light nuclei is as high as 3000 TeV or rather as low as a few hundred TeV has very important consequences on the supernova remnant paradigm for the origin of cosmic rays, as well on the crucial issue of the transition from Galactic to extragalactic cosmic rays. In such a complex phenomenological situation, it is important to have a clear picture of what is really known and what is not. Here I will discuss some solid and less solid aspects of the theory (or theories) for the origin of cosmic rays and the implications for future searches in this field. © 2014 Elsevier B.V.

Donnert J.M.F.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2014

Simulations of isolated binarymergers of galaxy clusters are a useful tool to study the evolution of these objects. For exceptionally massive systems, they even represent the only viable way of simulation, because these are rare in typical cosmological simulations. We present a new practical model for these simulations based on the Hernquist dark matter profile. The hydrostatic equation is solved for a beta-model with β = 2/3 in this potential and approximate expressions for X-ray brightness and Compton-y parameter are derived.We show in detail how to setup such a system using smoothed particle hydrodynamics. The theoretical and several numerical models are compared to observed scaling relations of galaxy clusters and satisfactory agreement with the self-similar relations is found. The model is then applied to investigate the observed cluster ACT-CT J0102-4915 'El Gordo', a particularly massive merging highredshift cluster.We are able to reproduce the X-ray luminosity, Sunyaev-Zeldovich effect and dark matter core distance as well as the rough shape of the observed cluster for reasonable model parameters. The lack of sub-structure prevents us from obtaining the fluctuations observed in the wake of the system and we argue that the parent cluster of the system was highly disturbed even before the main merger observed today. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Bernardini F.,Wayne State University | Bernardini F.,National institute for astrophysics | Cackett E.M.,Wayne State University
Monthly Notices of the Royal Astronomical Society | Year: 2014

We conducted the first long-term (75 d) X-ray monitoring of the black hole low-mass X-ray binary V404 Cyg, with the goal of understanding and characterizing its variability during quiescence. The X-ray light curve of V404 Cyg shows several flares on time-scales of hours with a count rate change of a factor of about 5-8. The root-mean-square variability is Fvar = 57.0 ± 3.2 per cent. The first-order structure function is consistent with both a power spectrum of index -1 (flicker noise), or with a power spectrum of index 0 (white noise), implying that the light curve is variable on time-scales from days to months. The X-ray spectrum is well fitted by a power law with spectral index τ = 2.10-2.35, and we found that the spectral shape remains roughly constant as the flux changes. A constant spectral shape with respect to a change in the X-ray flux may favour a scenario in which the X-ray emission is dominated by synchrotron radiation produced in a jet. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Vazza F.,Hamburger Sternwarte | Vazza F.,National institute for astrophysics | Bruggen M.,Hamburger Sternwarte
Monthly Notices of the Royal Astronomical Society | Year: 2014

Radio relics in galaxy clusters are thought to be associated with powerful shock waves that accelerate particles via diffusive shock acceleration (DSA). Among the particles accelerated by DSA, relativistic protons should outnumber electrons by a large factor.While the relativistic electrons emit synchrotron emission detectable in the radio band, the protons interact with the thermal gas to produce gamma-rays in hadronic interactions. Using simple models for the propagation of shock waves through clusters, the distribution of thermal gas and the efficiency of DSA, we find that the resulting hadronic gamma-ray emission lies very close or above the upper limits from the Fermi data on nearby clusters. This suggests that the relative acceleration efficiency of electrons and protons is at odds with predictions from DSA. The inclusion of re-accelerated 'fossil' particles does not seem to solve the problem. Our study highlights a possible tension of the commonly assumed scenario for the formation of radio relics and we discuss possible solutions to the problem. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Germana C.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2012

Context. Recent results from the OPERA experiment reported a neutrino beam traveling faster than light. The challenging experiment measured the neutrino time of flight (TOF) over a baseline from the CERN to the Gran Sasso site, concluding that the neutrino beam arrives -60 ns earlier than a light ray would do. Because the result, if confirmed, has an enormous impact on science, it might be worth double-checking the time definitions with respect to the non-inertial system in which the neutrino travel time was measured. An observer with a clock measuring the proper time τ free of non-inertial effects is the one located at the solar system barycenter (SSB). Aims. Potential problems in the OPERA data analysis connected with the definition of the reference frame and time synchronization are emphasized. We aim to investigate the synchronization of non-inertial clocks on Earth by relating this time to the proper time of an inertial observer at SSB. Methods. The Tempo2 software was used to time-stamp events observed on the geoid with respect to the SSB inertial observer time. Results. Neutrino results from OPERA might carry the fingerprint of non-inertial effects because they are timed by terrestrial clocks. The CERN-Gran Sasso clock synchronization is accomplished by applying corrections that depend on special and general relativistic time dilation effects at the clocks, depending on the position of the clocks in the solar system gravitational well. As a consequence, TOF distributions are centered on values shorter by tens of nanoseconds than expected, integrating over a period from April to December, longer if otherwise. It is worth remarking that the OPERA runs have always been carried out from April/May to November. Conclusions. If the analysis by Tempo2 holds for the OPERA experiment, the excellent measurement by the OPERA collaboration will turn into a proof of the general relativity theory in a weak field approximation. The analysis presented here is falsifiable because it predicts that performing the experiment from January to March/April, the neutrino beam will be detected to arrive -50 ns later than light. © ESO, 2012.

Bondi M.,National institute for astrophysics | Perez-Torres M.A.,Institute Astrofisica Of Andalucia Csic | Herrero-Illana R.,Institute Astrofisica Of Andalucia Csic | Alberdi A.,Institute Astrofisica Of Andalucia Csic
Astronomy and Astrophysics | Year: 2012

Context. The nuclear region of the luminous infrared galaxy (LIRG) Arp 299-A hosts a recent (? 10 Myr) intense burst of massive star formation that is expected to lead to numerous core-collapse supernovae (CCSNe). Previous VLBI observations, carried out with the European VLBI Network (EVN) at 5.0 GHz and with the VLBA at 2.3 and 8.4 GHz, resulted in the detection of many compact, bright, non-thermal sources in a region ? 150 pc in size. Aims. We aim to establish the nature of all non-thermal compact components in Arp 299-A, as well as to estimate its core-collapse supernova rate. While the majority of the compact components are expected to be young radio supernovae (RSNe) and supernova remnants (SNRs), a definitive classification is still lacking. Yet, this is very relevant for eventually establishing the CCSN rate, as well as the star formation rate, for this galaxy. Methods. We used multi-epoch EVN observations taken at 5.0 GHz to image the compact radio sources in the nuclear region of Arp 299-A with milliarcsecond resolution. We also used one single-epoch 5.0 GHz Multi-Element Radio Linked Interferometer Network (MERLIN) observation to image the extended emission in which these compact radio sources are embedded. Results. We present the first 5.0 GHz radio light-curve (spanning ∼2.5 yr) of all compact components in the nuclear starburst of Arp 299-A. Twenty-six compact sources are detected, eight of which are new objects. The properties of all detected objects are consistent with them being a mixed population of CCSNe and SNRs. We find clear evidence for at least two new CCSNe, implying a lower limit to the CCSN rate of ν SN ≥ 0.80 SN/yr, indicating that the bulk of the current star formation in Arp 299-A is taking place in the innermost ∼150 pc.A few more objects show variability consistent with them being recently exploded SNe, but only future observations will clarify this point. Our MERLIN observations trace a region of diffuse extended emission that is cospatial to the region where all compact sources are found. From this diffuse non-thermal radio emission traced by MERLIN we obtain an independent estimate for the CCSN rate, which is in the range ν SN = 0.40-0.65 SN/yr, in agreement with previous estimates and our direct estimate of the CCSN rate from the compact radio emission. Conclusions. Our ∼2.5 yr monitoring of Arp 299-A has allowed us to obtain for the first time a direct estimate of the CCSN rate of ν SN ≥ 0.80 SN/yr for the innermost ∼150 pc of Arp 299-A. © ESO, 2012.

Vazza F.,Hamburger Sternwarte | Vazza F.,National institute for astrophysics | Bruggen M.,Hamburger Sternwarte | Gheller C.,CSCS | Wang P.,NVDIA
Monthly Notices of the Royal Astronomical Society | Year: 2014

The amplification of primordial magnetic fields via a small-scale turbulent dynamo during structure formation might be able to explain the observed magnetic fields in galaxy clusters. The magnetization of more tenuous large-scale structures such as cosmic filaments is more uncertain, as it is challenging for numerical simulations to achieve the required dynamical range. In this work, we present magnetohydrodynamical cosmological simulations on large uniform grids to study the amplification of primordial seed fields in the intracluster medium (ICM) and in the warm-hot-intergalactic medium (WHIM). In the ICM, we confirm that turbulence caused by structure formation can produce a significant dynamo amplification, even if the amplification is smaller than what is reported in other papers. In the WHIM inside filaments, we do not observe significant dynamo amplification, even though we achieve Reynolds numbers of Re ~ 200-300. The maximal amplification for large filaments is of the order of ~100 for the magnetic energy, corresponding to a typical field of a few ~nG starting from a primordial weak field of 10-10 G (comoving). In order to start a small-scale dynamo, we found that a minimum of ~102 resolution elements across the virial radius of galaxy clusters was necessary. In filaments we could not find a minimum resolution to set off a dynamo. This stems from the inefficiency of supersonic motions in the WHIM in triggering solenoidal modes and small-scale twisting of magnetic field structures. Magnetic fields this small will make it hard to detect filaments in radio observations. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

De Grijs R.,Peking University | Bono G.,University of Rome Tor Vergata | Bono G.,National institute for astrophysics
Astronomical Journal | Year: 2014

The accuracy of extragalactic distance measurements ultimately depends on robust, high-precision determinations of the distances to the galaxies in the local volume. Following our detailed study addressing possible publication bias in the published distance determinations to the Large Magellanic Cloud (LMC), here we extend our distance range of interest to include published distance moduli to M31 and M33, as well as to a number of their wellknown dwarf galaxy companions. We aim at reaching consensus on the best, most homogeneous, and internally most consistent set of Local Group distance moduli to adopt for future, more general use based on the largest set of distance determinations to individual Local Group galaxies available to date. Based on a careful, statistically weighted combination of the main stellar population tracers (Cepheids, RR Lyrae variables, and the magnitude of the tip of the red-giant branch), we derive a recommended distance modulus to M31 of (m - M) M31 0 = 24.46 ± 0.10 mag - adopting as our calibration an LMC distance modulus of (m - M)LMC 0 = 18.50 mag - and a fully internally consistent set of benchmark distances to key galaxies in the local volume, enabling us to establish a robust and unbiased, near-field extragalactic distance ladder. © 2014. The American Astronomical Society. All rights reserved.

Tissera P.B.,CONICET | Tissera P.B.,Institute Astronomia y Fisica del Espacio | Tissera P.B.,Andres Bello University | Beers T.C.,National institute for astrophysics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present a comprehensive study of the chemical properties of the stellar haloes of Milky Way mass galaxies, analysing the transition between the inner to the outer haloes. We find the transition radius between the relative dominance of the inner-halo and outer-halo stellar populations to be ̃15-20 kpc for most of our haloes, similar to that inferred for the Milky Way from recent observations. While the number density of stars in the simulated inner-halo populations decreases rapidly with distance, the outer-halo populations contribute about 20-40 per cent in the fiducial solar neighbourhood, in particular at the lowest metallicities. We have determined [Fe/H] profiles for our simulated haloes; they exhibit flat or mild gradients, in the range [-0.002, -0.01] dex kpc-1. The metallicity distribution functions exhibit different features, reflecting the different assembly history of the individual stellar haloes. We find that stellar haloes formed with larger contributions from massive subgalactic systems have steeper metallicity gradients. Very metal-poor stars are mainly contributed to the halo systems by lower mass satellites. There is a clear trend among the predicted metallicity distribution functions that a higher fraction of low-metallicity stars are found with increasing radius. These properties are consistent with the range of behaviours observed for stellar haloes of nearby galaxies. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Nataf D.M.,Australian National University | Cassisi S.,National institute for astrophysics | Athanassoula E.,Aix - Marseille University
Monthly Notices of the Royal Astronomical Society | Year: 2014

We demonstrate that failure to properly account for stellar evolution can bias results in determinations of the spatial morphology of Galactic bulge stars, focusing on the question of whether or not the X-shape is more pronounced among the more metal-rich stars than among the metalpoor stars. We argue that this trend, a result recently claimed by three separate groups, may have been overestimated as it is relatively easier to detect a bimodality in the distance distribution function at higher metallicities. This is due to three factors. First, the intrinsic colour of red clump and red giant stars varies with metallicity, at the level d(V- I)RC/d[M/H] ≈ 0.25 mag dex-1, and thus the ratio of red clump to red giant stars within a spectroscopic sample will depend on the photometric selection of any investigation. Secondly, the duration of ascent of the red giant branch goes down and the red clump lifetime goes up as metallicity increases, which has the effect of increasing the ratio of red clump to red giant stars by as much as ~33 per cent over the range of the bulge metallicity distribution function. Finally, over the same metallicity interval, the effective number of red giant branch bump stars is predicted to increase by ~200 per cent, and their presence becomes degenerate with the observational parameters of the two red clumps, creating an illusory increase in signal to noise for a second peak in the distance modulus distribution.© 2014 The Authors.

Vazza F.,Hamburger Sternwarte | Vazza F.,National institute for astrophysics | Gheller C.,CSCS | Bruggen M.,Hamburger Sternwarte
Monthly Notices of the Royal Astronomical Society | Year: 2014

Non-thermal (relativistic) particles are injected into the cosmos by structure formation shock waves, active galactic nuclei and stellar explosions. We present a suite of unigrid cosmological simulations (up to 20483) using a two-fluid model in the grid code ENZO. The simulations include the dynamical effects of cosmic ray (CR) protons and cover a range of theoretically motivated acceleration efficiencies. For the bulk of the cosmic volume the modelling of CR processes is rather stable with respect to resolution, provided that a minimum (cell) resolution of̃100 kpc h-1 is employed. However, the results for the innermost cluster regions depend on the assumptions for the baryonic physics. Inside clusters, non-radiative runs at high resolution tend to produce an energy density of CRs that are below available upper limits from the Fermi satellite, while the radiative runs are found to produce a higher budget of CRs. We show that weak (M ≤ 3-5) shocks and shock-re-acceleration are crucial to set the level of CRs in the innermost region of clusters, while in the outer regions the level of CR energy is mainly set via direct injection by stronger shocks, and is less sensitive to cooling and feedback from active galactic nuclei and supernovae. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.

Omand C.M.B.,University of Waterloo | Omand C.M.B.,University of British Columbia | Balogh M.L.,University of Waterloo | Balogh M.L.,Leiden University | Poggianti B.M.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2014

Using data from the Sloan Digital Sky Survey (SDSS)-DR7, including structural measurements from 2D surface brightness fits with GIM2D, we show how the fraction of quiescent galaxies depends on galaxy stellar mass M*, effective radius Re, fraction of r-band light in the bulge, B/T, and their status as a central or satellite galaxy at 0.01 < z < 0.2. For central galaxies we confirm that the quiescent fraction depends not only on stellar mass, but also on Re. The dependence is particularly strong as a function of M*/Rα e , with α ̃ 1.5. This appears to be driven by a simple dependence on B/T over the mass range 9 < log (M*/M⊙) < 11.5, and is qualitatively similar even if galaxies with B/T > 0.3 are excluded. For satellite galaxies, the quiescent fraction is always larger than that of central galaxies, for any combination of M*, Re and B/T. The quenching efficiency is not constant, but reaches amaximum of̃0.7 for galaxies with 9 < log (M*/M⊙) < 9.5 and Re < 1 kpc. This is the same region of parameter space in which the satellite fraction itself reaches its maximum value, suggesting that the transformation from an active central galaxy to a quiescent satellite is associated with a reduction in Re due to an increase in dominance of a bulge component. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Fiorentino G.,National institute for astrophysics | Monelli M.,Institute of Astrophysics of Canarias | Monelli M.,University of La Laguna
Astronomy and Astrophysics | Year: 2012

Context. The properties of variable stars can give independent constraints on the star formation history of the host galaxy, by determining the age and metallicity of the parent population. Aims. We investigate the pulsation properties of 84 Anomalous Cepheids (ACs) detected by the OGLE-III survey in the Large Magellanic Cloud (LMC), in order to understand the formation mechanism and the characteristics of the parent population they came from. Methods. We used an updated theoretical pulsation scenario to derive the mass and the pulsation mode of each AC in the sample. We also used a Kolmogorov-Smirnov test to analyze the spatial distribution of the ACs, in comparison with that of other groups of variable stars, and connect their properties with the star formation history of the LMC. Results. We find that the mean mass of ACs is 1.2 ± 0.2 M ȯ. We show that ACs do not follow the same spatial distribution of classical Cepheids. This and the difference in their period-luminosity relations further support the hypothesis that ACs are not the extension to low luminosity of classical Cepheids. The spatial distribution of ACs is also different from that of bona-fide tracers of the old population, such as RR Lyrae stars and population II Cepheids. We therefore suggest that the majority of ACs in the LMC are made of intermediate-age (1-6 Gyr), metal-poor single stars. Finally, we investigate the relation between the frequency of ACs and the luminosity of the host galaxy, disclosing that purely old systems follow a very tight relation and that galaxies with strong intermediate-age and young star formation tend to have an excess of ACs, in agreement with their hosting ACs formed via both single and binary star channels. © 2012 ESO.

Lanza A.F.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2012

Context. Late-type stars interact with their close-in planets through their coronal magnetic fields. Aims. We introduce a theory for the interaction between the stellar and planetary fields focussing on the processes that release magnetic energy in the stellar coronae. Methods. We consider the energy dissipated by the reconnection between the stellar and planetary magnetic fields as well as that made available by the modulation of the magnetic helicity of the coronal field produced by the orbital motion of the planet. We estimate the powers released by both processes in the case of axisymmetric and non-axisymmetric, linear and non-linear force-free coronal fields finding that they scale as B 0 4/3 B p0 2/3 R p 2 v rel, where B 0 is the mean stellar surface field, B p0 the planetary field at the poles, R p the radius of the planet, and v rel the relative velocity between the stellar and the planetary fields. Results. A chromospheric hot spot or a flaring activity phased to the orbital motion of the planet are found only when the stellar field is axisymmetric. In the case of a non-axisymmetric field, the time modulation of the energy release is multiperiodic and can be easily confused with the intrinsic stellar variability. We apply our theory to the systems with some reported evidence of star-planet magnetic interaction finding a dissipated power at least one order of magnitude smaller than that emitted by the chromospheric hot spots. The phase lags between the planets and the hot spots are reproduced by our models in all the cases except for υ And. Conclusions. The chromospheric hot spots rotating in phase with the planets cannot be explained by the energy dissipation produced by the interaction between stellar and planetary fields as considered by our models and require a different mechanism. © 2012 ESO.

Battinelli P.,National institute for astrophysics | Demers S.,University of Montreal
Astronomy and Astrophysics | Year: 2012

Context. Carbon stars are among the brightest intermediate-age stars. Over one hundred have been identified in the Galactic halo. Since the halo consists essentially in an old stellar population, we believe that these C stars are trespassers and belong to streams left over by disrupted dwarf spheroidal galaxies. Aims. By performing photometric monitoring we intend to detect long-period variables among halo carbon stars. We should be in position to identify Mira, semi-regular, and irregular variables and determine their period and age group. Methods. We obtained, over several semesters, K, J, and I images centered on the C stars in order to determine their variation and periodicity. Results. We establish the period of 14 program stars and discover 13 Miras among them. Most of them belong to the 1-3 Gyr age group. Conclusions. The period distribution of the halo Miras closely matches that of the Miras of Fornax. The lack of old Miras suggests that the majority of the halo Miras likely do not originate from the Sagittarius dwarf spheroidal galaxy, which is believed to be older than 5 Gyr. © 2012 ESO.

Lebzelter T.,University of Vienna | Uttenthaler S.,University of Vienna | Busso M.,University of Perugia | Schultheis M.,Observatoire de Besancon | Aringer B.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2012

Context. A small number of K-type giants on the red giant branch (RGB) is known to be very rich in lithium (Li). This fact is not accounted for by standard stellar evolution theory. The exact phase and mechanism of Li enrichment is still a matter of debate. Aims. Our goal is to probe the abundance of Li along the RGB, from its base to the tip, to confine Li-rich phases that are supposed to occur on the RGB. Methods. For this end, we obtained medium-resolution spectra with the FLAMES spectrograph at the VLT in GIRAFFE mode for a large sample of 401 low-mass RGB stars located in the Galactic bulge. The Li abundance was measured in the stars with a detectable Li 670.8 nm line by means of spectral synthesis with COMARCS model atmospheres. A new 2MASS (J-K S)-T eff calibration from COMARCS models is presented in the Appendix. Results. Thirty-one stars with a detectable Li line were identified, three of which are Li-rich according to the usual criterion (logε(Li) > 1.5). The stars are distributed all along the RGB, not concentrated in any particular phase of the red giant evolution (e.g. the luminosity bump or the red clump). The three Li-rich stars are clearly brighter than the luminosity bump and red clump, and do not show any signs of enhanced mass loss. Conclusions. We conclude that the Li enrichment mechanism cannot be restricted to a clearly defined phase of the RGB evolution of low-mass stars (M ∼ 1 M ⊙), contrary to earlier suggestions from disk field stars. © 2012 ESO.

Lanza A.F.,National institute for astrophysics | Shkolnik E.L.,Lowell Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2014

Recent analyses of Kepler space telescope data reveal that transiting planets with orbital periods shorter than 2-3 d are generally observed around late-type stars with rotation periods longer than ~5-10 d. We investigate different explanations for this phenomenon and favour an interpretation based on secular perturbations in multiplanet systems on non-resonant orbits. In those systems, the orbital eccentricity of the innermost planet can reach values close to unity through a process of chaotic diffusion of its orbital elements in the phase space. When the eccentricity of the innermost orbit becomes so high that the periastron gets closer than ~0.05 au, tides shrink and circularize the orbit producing a close-in planet on a time-scale ≲50 Myr. The probability of high eccentricity excitation and subsequent circularization is estimated and is found to increase with the age of the system. Thus, we are able to explain the observed statistical correlation between stellar rotation and minimum orbital period of the innermost planet by using the stellar rotation period as a proxy of its age through gyrochronology. Moreover, our model is consistent with the entire observed distributions of the rotation and orbital periods Porb for 3 ≲ Porb ≲ 15 d. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Rivera-Ingraham A.,University of Toronto | Martin P.G.,University of Toronto | Polychroni D.,National institute for astrophysics | Moore T.J.T.,Liverpool John Moores University
Astrophysical Journal | Year: 2011

In this work, we have carried out an in-depth analysis of the young stellar content in the W3 giant molecular cloud (GMC). The young stellar object (YSO) population was identified and classified in the Infrared Array Camera/Multiband Imaging Photometer color-magnitude space according to the "Class" scheme and compared to other classifications based on intrinsic properties. Class0/I and II candidates were also compared to low-/intermediate-mass pre-main-sequence (PMS) stars selected through their colors and magnitudes in the Two Micron All Sky Survey. We find that a reliable color/magnitude selection of low-mass PMSstars in the infrared requires prior knowledge of the protostar population, while intermediate-mass objects can be more reliably identified. By means of the minimum spanning tree algorithm and our YSOspatial distribution and age maps, we investigated the YSOgroups and the star formation history in W3. We find signatures of clustered and distributed star formation in both triggered and quiescent environments. The central/western parts of the GMC are dominated by large-scale turbulence likely powered by isolated bursts of star formation that triggered secondary star formation events. Star formation in the eastern high-density layer (HDL) also shows signs of quiescent and triggered stellar activity, as well as extended periods of star formation. While our findings support triggering as a key factor for inducing and enhancing some of the major star-forming activity in the HDL (e.g., W3 Main/W3(OH)), we argue that some degree of quiescent or spontaneous star formation is required to explain the observed YSOpopulation. Our results also support previous studies claiming a spontaneous origin for the isolated massive star(s) powering KR140. © 2011. The American Astronomical Society. All rights reserved.

Turolla R.,University of Padua | Turolla R.,University College London | Zane S.,University College London | Pons J.A.,University of Alicante | And 2 more authors.
Astrophysical Journal | Year: 2011

SGR0418+5729 is a transient soft gamma-ray repeater which underwent amajor outburst in 2009 June, during which the emission of short bursts was observed. Its properties appeared quite typical of other sources of the same class until long-term X-raymonitoring failed to detect any period derivative. The present upper limit on Ṗ implies that the surface dipole field is Bp ≤ 7.5×1012 G, well below those measured in other soft gamma-ray repeaters (SGRs) and in the Anomalous X-ray Pulsars (AXPs), a group of similar sources. Both SGRs and AXPs are currently believed to be powered by ultra-magnetized neutron stars (magnetars, Bp ≈ 10 141015 G). SGR 0418+5729 hardly seems to fit in such a picture. We show that the magneto-rotational properties of SGR 0418+5729 can be reproduced if this is an aged magnetar, ≈1 Myr old, which experienced substantial field decay. The large initial toroidal component of the internal field required to match the observed properties of SGR 0418+5729 ensures that crustal fractures, and hence bursting activity, can still occur at the present time. The thermal spectrum observed during the outburst decay is compatible with the predictions of a resonant Compton scattering model (as in other SGRs/AXPs) if the field is low and the magnetospheric twist is moderate. © 2011. The American Astronomical Society. All rights reserved.

Rephaeli Y.,Tel Aviv University | Rephaeli Y.,University of California at San Diego | Arieli Y.,Tel Aviv University | Persic M.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

Measurement sensitivity in the energetic γ-ray region has improved considerably and is about to increase further in the near future, motivating a detailed calculation of high-energy (HE; ≥100 MeV) and very high-energy (VHE; ≥100 GeV) γ-ray emission from the nearby starburst galaxy NGC 253. Adopting the convection-diffusion model for energetic electron and proton propagation, and accounting for all the relevant hadronic and leptonic processes, we determine the steady-state energy distributions of these particles by a detailed numerical treatment. The electron distribution is directly normalized by the measured synchrotron radio emission from the central starburst region; a commonly expected theoretical relation is then used to normalize the proton spectrum in this region. Doing so fully specifies the electron spectrum throughout the galactic disc and, with an assumed spatial profile of the magnetic field, the predicted radio emission from the full disc matches well the observed spectrum, confirming the validity of our treatment. The resulting radiative yields of both particles are calculated; the integrated HE and VHE fluxes from the entire disc are predicted to be f(≥100 MeV) ≃ (1.8 +1.5 -0.8) × 10-8 cm-2 s -1 and f(≥100 GeV) ≃ (3.6+3.4 -1.7) × 10-12 cm-2 s-1, with a central magnetic field value B0 ≃ 190 ± 10 μG. We discuss the feasibility of measuring emission at these levels with the space-borne Fermi and ground-based Cherenkov telescopes. © 2009 RAS.

Amato E.,National institute for astrophysics
International Journal of Modern Physics D | Year: 2014

Initial discovery of Cosmic Rays (CRs) dates back to a century ago (1912). Their identification as particles rather than radiation dates to about 20 years later and in 20 more years also the first suggestion that they were associated with SNRs was in place. The basic mechanism behind their acceleration was suggested almost 40 years ago. Much work has been done since then with regard to the aim of proving that both the acceleration mechanism and site are well-understood, but no definite proof has been obtained: in spite of impressive progress of both theory and observations, the evidence in support of the commonly accepted interpretation is only circumstantial. In the following, I will try to make the point on where we stand in terms of how our theories confront with data. I will review recent progress on the subject and try pointing the avenues to pursue in order to gather new proofs, if not a smoking gun evidence of the origin of Galactic CRs. © 2014 World Scientific Publishing Company.

Koulouridis E.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2014

We present a study of the local environment (≤200 h-1 kpc) of 31 hidden broad line region (HBLR) and 43 non-HBLR Seyfert 2 (Sy2) galaxies in the nearby universe (z ≤ 0.04). To compare our findings, we constructed two control samples that match the redshift and the morphological type distribution of the HBLR and non-HBLR samples. We used the NASA Extragalactic Database (NED) to find all neighboring galaxies within a projected radius of 200 h-1 kpc around each galaxy, and a radial velocity difference Δu ≤ 500 km?s-1. Using the digitized Schmidt survey plates (DSS) and/or the Sloan Digital Sky Survey (SDSS), when available, we confirmed that our sample of Seyfert companions is complete. We find that, within a projected radius of at least 150 h-1 kpc around each Seyfert, the fraction of non-HBLR Sy2 galaxies with a close companion is significantly higher than that of their control sample, at the 96% confidence level. Interestingly, the difference is due to the high frequency of mergers in the non-HBLR sample, seven versus only one in the control sample, while they also present a high number of hosts with signs of peculiar morphology. In sharp contrast, the HBLR sample is consistent with its control sample. Furthermore, the number of the HBLR host galaxies that present peculiar morphology, which probably implies some level of interactions or merging in the past, is the lowest in all four galaxy samples. Given that the HBLR Sy2 galaxies are essentially Seyfert 1 (Sy1) with their broad line region (BLR) hidden because of the obscuring torus, while the non-HBLR Sy2 galaxies probably also include true Sy2s that lack the BLR as well as heavily obscured objects that prevent even the indirect detection of the BLR, our results are discussed within the context of an evolutionary sequence of activity triggered by close galaxy interactions and merging. We argue that the non-HBLR Sy2 galaxies may represent different stages of this sequence, possibly the beginning and the end of the nuclear activity.

Carbillet M.,University of Nice Sophia Antipolis | Riccardi A.,National institute for astrophysics
Applied Optics | Year: 2010

We describe new solutions permitting us to overcome the well-known problems encountered when employing the two main classical methods for numerical modeling of atmospherically perturbed phase screens. The first method, the fast-Fourier-transform-based numerical method, suffers from a lack of low frequencies. Subharmonics adding is an already-known solution to this problem, but no criterion has been defined up to now in order to precisely determine how many subharmonics are necessary for each given case ofphysical and numerical characteristics. We define two criteria and show their practical efficiency. The second, Zernike-based, method suffers, a contrario, from bad behavior of the phase screens at high spatial frequencies. To overcome this problem, due to numerical instability, we developed an algorithm based on an alternative definition of the Zernike polynomials, involving the recurrence definition of the Jacobi polynomials, as well as the relationship between the Zernike and the Jacobi polynomials. The methods described and used in this paper have been implemented within the freely distributed software package CAOS. © 2010 Optical Society of America.

Martel H.,Laval University | Barai P.,National institute for astrophysics
Astrophysical Journal | Year: 2012

We combine an N-body simulation algorithm with a subgrid treatment of galaxy formation, mergers, and tidal destruction, and an observed conditional luminosity function Φ(L|M), to study the origin and evolution of galactic and extragalactic light inside a cosmological volume of size (100 Mpc) 3, in a concordance ΛCDM model. This algorithm simulates the growth of large-scale structures and the formation of clusters, the evolution of the galaxy population in clusters, the destruction of galaxies by mergers and tides, and the evolution of the intracluster light (ICL). We find that destruction of galaxies by mergers dominates over destruction by tides by about an order of magnitude at all redshifts. However, tidal destruction is sufficient to produce ICL fractions f ICL that are sufficiently high to match observations. Our simulation produces 18 massive clusters (Mcl > 1014 M⊙) with values of fICL ranging from 1% to 58% at z = 0. There is a weak trend of fICL to increase with cluster mass. The bulk of the ICL (∼60%) is provided by intermediate galaxies of total masses 1011-1012 M⊙ and stellar masses 6 × 108 M⊙ to 3 × 10 10 M⊙ that were tidally destroyed by even more massive galaxies. The contribution of low-mass galaxies to the ICL is small and the contribution of dwarf galaxies is negligible, even though, by numbers, most galaxies that are tidally destroyed are dwarfs. Tracking clusters back in time, we find that their values of f ICL tend to increase over time, but can experience sudden changes that are sometimes non-monotonic. These changes occur during major mergers involving clusters of comparable masses but very different intracluster luminosities. Most of the tidal destruction events take place in the central regions of clusters. As a result, the ICL is more centrally concentrated than the galactic light. Our results support tidal destruction of intermediate-mass galaxies as a plausible scenario for the origin of the ICL. © 2012. The American Astronomical Society. All rights reserved.

Andreon S.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2015

Richness, i.e., the number of bright cluster galaxies, is known to correlate with the cluster mass, however, to exploit it as mass proxy we need a way to estimate the aperture in which galaxies should be counted that minimizes the scatter between mass and richness. In this work, using a sample of 39 clusters with accurate caustic masses at 0.1

Marcon-Uchida M.M.,University of Trieste | Marcon-Uchida M.M.,University of Sao Paulo | Matteucci F.,University of Trieste | Matteucci F.,National institute for astrophysics | Costa R.D.D.,University of Sao Paulo
Astronomy and Astrophysics | Year: 2010

Context. The distribution of chemical abundances and their variation with time are important tools for understanding the chemical evolution of galaxies. In particular, the study of chemical evolution models can improve our understanding of the basic assumptions made when modelling our Galaxy and other spirals. Aims. We test a standard chemical evolution model for spiral disks in the Local Universe and study the influence of a threshold gas density and different efficiencies in the star formation rate (SFR) law on radial gradients of abundance, gas, and SFR. The model is then applied to specific galaxies. Methods. We adopt a one-infall chemical evolution model where the Galactic disk forms inside-out by means of infall of gas, and we test different thresholds and efficiencies in the SFR. The model is scaled to the disk properties of three Local Group galaxies (the Milky Way, M 31 and M 33) by varying its dependence on the star formation efficiency and the timescale for the infall of gas onto the disk. Results. Using this simple model, we are able to reproduce most of the observed constraints available in the literature for the studied galaxies. The radial oxygen abundance gradients and their time evolution are studied in detail. The present day abundance gradients are more sensitive to the threshold than to other parameters, while their temporal evolutions are more dependent on the chosen SFR efficiency. A variable efficiency along the galaxy radius can reproduce the present day gas distribution in the disk of spirals with prominent arms. The steepness in the distribution of stellar surface density differs from massive to lower mass disks, owing to the different star formation histories. Conclusions. The most massive disks seem to have evolved faster (i.e., with more efficient star formation) than the less massive ones, thus suggesting a downsizing in star formation for spirals. The threshold and the efficiency of star formation play a very important role in the chemical evolution of spiral disks. For instance, an efficiency varying with radius can be used to regulate the star formation. The oxygen abundance gradient can steepen or flatten in time depending on the choice of this parameter. © 2010 ESO.

Terzo S.,University of Palermo | Reale F.,University of Palermo | Reale F.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2010

Aims. Using TRACE coronal observations, we compare the analysis and diagnostics of coronal loop after subtracting the background with two different and independent methods. Methods. We analyze sequences of images in the 171 Ã and 195 Ã filter bands of TRACE. One background subtraction method consists of considering background values obtained by interpolating between concentric strips around the analyzed loop. Another involves a pixel-to-pixel subtraction of the final image after the loop has completely faded out, used by Reale and Ciaravella. Results. We compare the emission distributions along the loop obtained with the two methods and find that they differ considerably. We also find differences in the related filter ratio and temperature profiles. In particular, the pixel-to-pixel subtraction leads to coherent diagnostics of a cooling loop. After applying the other type of subtraction, the diagnostics are much less clear. Conclusions. The background subtraction should be treated with care when analyzing a loop. The pixel-to-pixel subtraction appears to be more reliable, but its application is not always possible. Subtraction by means of interpolation between surrounding regions can produce higher systematic errors, because of intersecting structures and the large amount of subtracted emission in TRACE observations. © ESO, 2010.

La Barbera F.,National institute for astrophysics | De Carvalho R.R.,National Institute for Space Research | De La Rosa I.G.,Institute of Astrophysics of Canarias | De La Rosa I.G.,University of La Laguna | Lopes P.A.A.,Federal University of Rio de Janeiro
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present a complete analysis of the Fundamental Plane (FP) of early-type galaxies (ETGs) in the nearby Universe (z < 0.1). The sample, as defined in Paper I, comprises 39 993 ETGs located in environments covering the entire domain in local density (from field to cluster). We derive the FP in the grizYJHK wavebands with a detailed discussion on fitting procedure, bias due to selection effects and bias due to correlated errors on the effective parameters, r e and 〈μ〉 e, as key factors in obtaining meaningful FP coefficients. Studying the Kormendy relation (KR) we find that its slope varies from g (3.44 ± 0.04) through K (3.80 ± 0.02) implying that smaller size ETGs have a larger ratio of optical to near-infrared (NIR) radii than galaxies with larger r e. We also examine the Faber-Jackson (FJ) relation and find that its slope is similar for all wavebands, within the uncertainties, with a mean value of 0.198 ± 0.007. Writing the FP equation as log r e=a log σ 0+b〈μ〉 e+c, we find that the 'a' varies from 1.38 ± 0.02 in g to 1.55 ± 0.02 in K, implying a 12 per cent variation across the grizYJHK wavelength baseline. The corresponding variation of 'b' is negligible (b~ 0.316), while 'c' varies by ~10 per cent. We show that the waveband dependence of the FJ and KR results from the complex variation of the distribution of galaxies in the face-on projection of the FP as well as by the change of FP coefficients with waveband. We find that 'a' and 'b' become smaller for higher Sersic index and larger axial ratios, independent of the waveband. This suggests that these variations are likely to be related to differences in structural and dynamical (rather than stellar population) properties of ETGs. It is noticeable that galaxies with bluer colours and disc-like isophotes have smaller 'b', with the effect decreasing smoothly from g through K. Considering a power-law relation between mass-to-light ratio and (dynamical) mass, M/L M γ, we estimate γ from the FP coefficients in grizYJHK. The γ decreases from 0.224 ± 0.008 in g to 0.186 ± 0.009 in K band. Using the γ values, we estimate the variation of age and metallicity of the stellar populations present in massive galaxies per decade in stellar mass. This analysis shows that in the NIR the tilt of the FP is not due to stellar population variation, and that ETGs have coeval stellar populations with an age variation of a few per cent per decade in mass, and a corresponding metallicity increase of ~23 per cent. We also show that current semi-analytical models of galaxy formation reproduce very well these amounts of variation of age and metallicity with respect to stellar mass. © 2010 The Authors. Journal compilation © 2010 RAS.

In physically inviscid fluid dynamics, 'shock-capturing' methods adopt either an artificial viscosity contribution or an appropriate Riemann-solver algorithm. These techniques are necessary to solve the strictly hyperbolic Euler equations if flow discontinuities (the Riemann problem) are to be solved. A necessary dissipation is normally used in such cases. An explicit artificial viscosity contribution is normally adopted to smooth out spurious heating and to treat transport phenomena. Such a treatment of inviscid flows is also widely adopted in the smooth particle hydrodynamics (SPH) finite-volume free Lagrangian scheme. In other cases, the intrinsic dissipation of Godunov-type methods is implicitly useful. Instead, 'shock-tracking' methods normally use the Rankine-Hugoniot jump conditions to solve such problems. A simple, effective solution of the Riemann problem in inviscid ideal gases is proposed here, based on a reformulation of the equation of state (EoS) in the Euler equations in fluid dynamics, the limit of which for a motionless gas coincides with the classical EoS of ideal gases. The application of such an effective solution to the Riemann problem excludes any dependence, in the transport phenomena, on particle-smoothing resolution length h in non-viscous SPH flows. Results for one-dimensional shock-tube tests, as well as examples of application for two-dimensional shear flows, are shown here. As an astrophysical application, a much better identification of spiral structures in accretion discs in a close binary (CB) as a result of this reformulation is also shown here. © 2010 The Author. Journal compilation © 2010 RAS.

Ventura P.,National institute for astrophysics | Marigo P.,University of Padua
Monthly Notices of the Royal Astronomical Society | Year: 2010

We investigate the main physical properties of low-metallicity asymptotic giant branch (AGB) stars with the aim of quantifying the uncertainties that presently affect the predicted chemical yields of these stars, associated with the mass-loss and description of molecular opacities. We find that above a threshold mass, M≃ 3.5M ⊙ for Z= 0.001, the results are little dependent on the opacity treatment, as long as the hot-bottom burning (HBB) prevents the surface C/O ratio from exceeding unity; the yields of these massive AGB stars are expected to be mostly determined by the efficiency of convection, with a relatively mild dependence on the mass-loss description. A much higher degree of uncertainty is associated with the yields of less-massive models, which critically depend on the adopted molecular opacities. An interval of masses exists, say, 2.0-3.0 M ⊙ (the exact range depends on the mass-loss), in which the HBB may be even extinguished following the cooling produced by the opacity of C-bearing molecules. The yields of these stars are the most uncertain, the variation range being the largest (up to ~2 dex) for the nitrogen and sodium yields. For very low mass models, not experiencing the HBB (M≥ 1.5 M ⊙), the description of mass-loss and the treatment of the convective boundaries are crucial for the occurrence of the third dredge-up, with a sizeable impact on the CNO yields. © 2010 The Authors. Journal compilation © 2010 RAS.

Lanzafame G.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

Adaptive spatial domains are currently used in smooth particle hydrodynamics (SPH) with the aim of performing better spatial interpolations, mainly for expanding or shock gas dynamics. In this work, we propose an SPH interpolating kernel reformulation, also suitable for treating free edge (FE) boundaries in the computational domain. Application to both inviscid and viscous stationary low compressibility accretion disc models in close binaries is shown. The investigation carried out in this paper is a consequence of the fact that low compressibility modelling is crucial for checking numerical reliability. Results show that physical viscosity supports well-bound accretion disc formation, despite the low gas compressibility, when a Gaussian-derived kernel (from the error function) is assumed, in an extended particle range - whose half-width at half-maximum is fixed to a constant h value - without any spatial restrictions on its radial interaction: Gaussian SPH in extended range (hereinafter GASPHER). At the same time, GASPHER ensures adequate particle interpolations at the boundary FEs. Both SPH and adaptive SPH (ASPH) methods lack accuracy if there are no constraints on the boundary conditions, in particular at the edge of the particle envelope: FE conditions. In SPH, an inefficient particle interpolation involves a few neighbour particles; however, in ASPH, non-physical effects involve both the boundary layer particles and the radial transport.A GASPHER scheme can be rightly adopted in troublesome physical regimes such as in a regime where FE conditions involve the computational domain, in viscous fluid dynamics or in both.Despite the low compressibiity condition applied, the viscous GASPHER model shows clear spiral pattern profiles demonstrating better quality of results compared to SPH viscous ones. Moreover, a successful comparison of results concerning a GASPHER 1D inviscid shock tube with an analytical solution is also reported. © 2010 The Author. Journal compilation © 2010 RAS.

Andreon S.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

The analysis of a sample of 52 clusters with precise and hypothesis-parsimonious measurements of mass, derived from caustics based on about 208 member velocities per cluster on average, shows that low-mass clusters and groups are not simple scaled-down versions of their massive cousins in terms of stellar content: lighter clusters have more stars per unit cluster mass. The same analysis also shows that the stellar content of clusters and groups displays an intrinsic spread at a given cluster mass, i.e. clusters are not similar to each other in the amount of stars they contain, not even at a fixed cluster mass. The stellar mass fraction depends on halo mass with (logarithmic) slope -0.55 ± 0.08 and with 0.15 ± 0.02 dex of intrinsic scatter at a fixed cluster mass. These results are confirmed by adopting masses derived from velocity dispersion. The intrinsic scatter at a fixed cluster mass we determine for gas mass fractions taken from literature is smaller, 0.06 ± 0.01 dex. The intrinsic scatter in both the stellar and gas mass fractions is a distinctive signature that individual regions from which clusters and groups collected matter, a few tens of Mpc wide, are not yet representative of the mean gas and baryon content of the Universe. The observed stellar mass fraction values are in marked disagreement with gasdynamics simulations with cooling and star formation of clusters and groups. Instead, the amplitude and cluster mass dependency of observed stellar mass fractions are those required not to need any active galactic nuclei (AGN) feedback to describe gas and stellar mass fractions and X-ray scale relations in simple semi-analytic cluster models. By adding stellar and gas masses and accounting for the intrinsic variance of both quantities, we found that the baryon fraction is fairly constant for clusters and groups with masses between 1013.7 and 1015.0 M⊙ and it is offset from the WMAP-derived value by about 6σ. The offset is unlikely to be due to an underestimate of the stellar mass fraction, and could be related to the possible non-universality of the baryon fraction, pointed out by our measurements of the intrinsic scatter. Our analysis is the first that does not assume that clusters are identically equal at a given halo mass and it is also more accurate in many aspects. The data and code used for the stochastic computation are distributed with the paper. © 2010 The Author. Journal compilation © 2010 RAS.

Salvaterra R.,University of Insubria | Devecchi B.,University of Insubria | Colpi M.,University of Milan Bicocca | D'Avanzo P.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

Short gamma-ray bursts (SGRBs) are expected to form from the coalescence of compact binaries, either from primordial origin or from dynamical interactions in globular clusters. In this paper, we investigate the possibility that the offset and afterglow brightness of an SGRB can help in revealing the origin of its progenitor binary. We find that an SGRB is likely to result from the primordial channel if it is observed within 10 kpc from the centre of a massive galaxy and shows a detectable afterglow. The same conclusion holds if it is 100 kpc away from a small, isolated galaxy and shows a weak afterglow. On the other hand, a dynamical origin is suggested for those SGRBs with observable afterglow either at a large separation from a massive, isolated galaxy or with an offset of 10-100 kpc from a small, isolated galaxy. We discuss the possibility that SGRBs from the dynamical channel are hosted in intracluster globular clusters and find that GRB 061201 may fall within this scenario. © 2010 The Authors. Journal compilation © 2010 RAS.

Buson L.M.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2010

Context. The very center (r

Kappeler F.,Karlsruhe Institute of Technology | Gallino R.,University of Turin | Gallino R.,National institute for astrophysics | Bisterzo S.,University of Turin | Aoki W.,Japan National Astronomical Observatory
Reviews of Modern Physics | Year: 2011

Nucleosynthesis in the s process takes place in the He-burning layers of low-mass asymptotic giant branch (AGB) stars and during the He- and C-burning phases of massive stars. The s process contributes about half of the element abundances between Cu and Bi in solar system material. Depending on stellar mass and metallicity the resulting s-abundance patterns exhibit characteristic features, which provide comprehensive information for our understanding of the stellar life cycle and for the chemical evolution of galaxies. The rapidly growing body of detailed abundance observations, in particular, for AGB and post-AGB stars, for objects in binary systems, and for the very faint metal-poor population represents exciting challenges and constraints for stellar model calculations. Based on updated and improved nuclear physics data for the s-process reaction network, current models are aiming at an ab initio solution for the stellar physics related to convection and mixing processes. Progress in the intimately related areas of observations, nuclear and atomic physics, and stellar modeling is reviewed and the corresponding interplay is illustrated by the general abundance patterns of the elements beyond iron and by the effect of sensitive branching points along the s-process path. The strong variations of the s-process efficiency with metallicity bear also interesting consequences for galactic chemical evolution. © 2011 American Physical Society.

Scarpa R.,Institute of Astrophysics of Canarias | Falomo R.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2010

Context. Stellar kinematics in the external regions of globular clusters can be used to probe the validity of Newton's law in the low acceleration regimes without the complication of non-baryonic dark matter. Indeed, in contrast to the case of galaxies, in globular clusters a systematic deviation of the velocity dispersion profile from the expected Keplerian falloff would be indicative of a breakdown of Newtonian dynamics rather than the existence of dark matter. Aims. We perform a detailed analysis of the velocity dispersion in the globular cluster ω Centauri to determine whether it decreases monotonically with distance as expected within the framework of Newtonian dynamics, or whether it converges toward a constant value as recent works suggest. Methods. We combine measurements from two previous studies to almost double the data available at large radii, to better constrain the velocity dispersion profile in the low acceleration regime. Results. We found the inner region of ω Centauri is clearly rotating, while the rotational velocity tends to vanish, being consistent with no rotation at all in the external regions. The cluster velocity dispersion at large radii from the center is found to clearly deviate from the Newtonian prediction. Conclusions. We conclude that there are strong similarities between globular clusters and elliptical galaxies, for in both classes of objects the velocity dispersion tends to remain constant at large radii. In the case of galaxies, this is ascribed to the existence of a massive halo of dark matter, which is physically unlikely in the case of globular clusters. This similarity, if confirmed, is best explained by a breakdown of Newtonian dynamics below a critical acceleration. © 2010 ESO.

Capria M.T.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Cremonese G.,National institute for astrophysics | De Sanctis M.C.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Astronomy and Astrophysics | Year: 2010

Aims. On October 24, 2007 the comet 17P/ Holmes underwent an outburst that was extraordinary in both duration and size. We attempted to determine the cause of the outburst by acquiring and analyzing high resolution spectra of the comet. Methods. On two nights, October 25 and December 2, we acquired four high resolution spectra in the visible range at the Telescopio Nazionale Galileo in La Palma. The oxygen lines intensity ratio was estimated for the observation performed on October 25, and computed for the observation performed on December 2. Results. Many emission lines were detected in the spectra, most of them attributable to C2, NH2, CN and CH. The atomic O green line and one of the red doublet lines were detected in a spectrum acquired on October 25. All the three atomic O lines were detected in a spectrum acquired on December 2. The value obtained for the first night, 0.1 ± 0.11, implies that the H2O molecule was the main parent of the emission lines, while the value obtained for the second night, 0.3 ± 0.1, implies that the main parent was CO or CO2 instead than H2O. Conclusions. Our results imply that in the days around the outburst the water production was exceptionally high for that heliocentric distance. By December, however, the behavior of 17P/ Holmes had returned to that of a comet orbiting at 2.6 AU from the Sun, in which state the activity is probably sustained mostly by gases more volatile than water, such as CO and CO2. © 2010 ESO.

Iodice E.,National institute for astrophysics
AIP Conference Proceedings | Year: 2010

NGC4650A is a polar disk galaxy: this is a peculiar object composed by a central spheroidal component, the host galaxy (HG), and an extended disk made up by gas, stars and dust, which orbits nearly perpendicular to the plane of the central galaxy. The existence of two decoupled components of the angular momentum makes this object an ideal laboratory i) to study gravitational interactions and merging and ii) to constrain the 3D shape of its dark matter halo. In view of these applications, I will present two ongoing projects which aim to constrain i) the formation scenario for polar disks and ii) the dark halo content and shape, through a detailed analysis of the observed structure, metallicity and dynamics of NGC4650A. © 2010 American Institute of Physics.

Mignone A.,University of Turin | Tzeferacos P.,University of Turin | Bodo G.,National institute for astrophysics
Journal of Computational Physics | Year: 2010

We present and compare third- as well as fifth-order accurate finite difference schemes for the numerical solution of the compressible ideal MHD equations in multiple spatial dimensions. The selected methods lean on four different reconstruction techniques based on recently improved versions of the weighted essentially non-oscillatory (WENO) schemes, monotonicity preserving (MP) schemes as well as slope-limited polynomial reconstruction. The proposed numerical methods are highly accurate in smooth regions of the flow, avoid loss of accuracy in proximity of smooth extrema and provide sharp non-oscillatory transitions at discontinuities.We suggest a numerical formulation based on a cell-centered approach where all of the primary flow variables are discretized at the zone center. The divergence-free condition is enforced by augmenting the MHD equations with a generalized Lagrange multiplier yielding a mixed hyperbolic/parabolic correction, as in Dedner et al. [J. Comput. Phys. 175 (2002) 645-673]. The resulting family of schemes is robust, cost-effective and straightforward to implement. Compared to previous existing approaches, it completely avoids the CPU intensive workload associated with an elliptic divergence cleaning step and the additional complexities required by staggered mesh algorithms.Extensive numerical testing demonstrate the robustness and reliability of the proposed framework for computations involving both smooth and discontinuous features. © 2010 Elsevier Inc.

Donnarumma I.,National institute for astrophysics | Rossi E.M.,Leiden University
Astrophysical Journal | Year: 2015

Observational consequences of tidal disruption of stars by supermassive black holes (SMBHs) can enable us to discover quiescent SMBHs, constrain their mass function, and study the formation and evolution of transient accretion disks and jet formation. A couple of jetted tidal disruption events (TDEs) have been recently claimed in hard X-rays, challenging jet models, which were previously applied to γ-ray bursts and active galactic nuclei. It is therefore of paramount importance to increase the current sample. In this paper, we find that the best strategy is not to use upcoming X-ray instruments alone, which will yield between several (eRosita) and a couple of hundred (Einstein Probe) events per year below redshift one. We rather claim that a more efficient TDE hunter will be the Square Kilometer Array (SKA) operating in survey mode at 1.4 GHz. It may detect up to several hundred events per year below z ∼ 2.5 with a peak rate of a few tens per year at z ≈ 0.5. Therefore, even if the jet production efficiency is not 100% as assumed here, the predicted rates should be large enough to allow for statistical studies. The characteristic TDE decay of , however, is not seen in radio, whose flux emission is quite featureless. Identification therefore requires localization and prompt repointing by higher energy instruments. If radio candidates would be repointed within a day by future X-ray observatories (e.g., Athena- and LOFT-like missions), it will be possible to detect up to ≈400 X-ray counterparts, almost up to redshift 2. The shortcoming is that only for redshift below ≈0.4 will the trigger times be less than 10 days from the explosion. In this regard the X-ray surveys are better suited to probe the beginning of the flare, and are therefore complementary to SKA. © 2015. The American Astronomical Society. All rights reserved.

Mucciarelli A.,University of Bologna | Bellazzini M.,National institute for astrophysics | Merle T.,Free University of Colombia | Plez B.,French National Center for Scientific Research | And 2 more authors.
Astrophysical Journal | Year: 2015

We derive [K/Fe] abundance ratios for 119 stars in the globular cluster NGC 2808, all of them having O, Na, Mg, and Al abundances homogeneously measured in previous works. We detect an intrinsic star-to-star spread in the potassium abundance. Moreover [K/Fe] abundance ratios display statistically significant correlations with [Na/Fe] and [Al/Fe], and anti-correlations with [O/Fe] and [Mg/Fe]. All the four Mg deficient stars ([Mg/Fe] < 0.0) discovered so far in NGC 2808 are enriched in K by ∼0.3 dex with respect to those with normal [Mg/Fe]. NGC 2808 is the second globular cluster, after NGC 2419, where a clear Mg-K anti-correlation is detected, albeit of weaker amplitude. The simultaneous correlation/anti-correlation of [K/Fe] with all the light elements usually involved in the chemical anomalies observed in globular cluster stars strongly support the idea that these abundance patterns are due to the same self-enrichment mechanism that produces Na-O and Mg-Al anti-correlations. This finding suggests that detectable spreads in K abundances may be typical in the massive globular clusters where the self-enrichment processes are observed to produce their most extreme manifestations. © 2015. The American Astronomical Society. All rights reserved.

Scarlata C.,University of Minnesota | Panagia N.,US Space Telescope Science Institute | Panagia N.,National institute for astrophysics | Panagia N.,Supernova Ltd
Astrophysical Journal | Year: 2015

We present a semi-analytical line transfer model, (SALT), to study the absorption and re-emission line profiles from expanding galactic envelopes. The envelopes are described as a superposition of shells with density and velocity varying with the distance from the center. We adopt the Sobolev approximation to describe the interaction between the photons escaping from each shell and the remainder of the envelope. We include the effect of multiple scatterings within each shell, properly accounting for the atomic structure of the scattering ions. We also account for the effect of a finite circular aperture on actual observations. For equal geometries and density distributions, our models reproduce the main features of the profiles generated with more complicated transfer codes. Also, our SALT line profiles nicely reproduce the typical asymmetric resonant absorption line profiles observed in starforming/starburst galaxies whereas these absorption profiles cannot be reproduced with thin shells moving at a fixed outflow velocity. We show that scattered resonant emission fills in the resonant absorption profiles, with a strength that is different for each transition. Observationally, the effect of resonant filling depends on both the outflow geometry and the size of the outflow relative to the spectroscopic aperture. Neglecting these effects will lead to incorrect values of gas covering fraction and column density. When a fluorescent channel is available, the resonant profiles alone cannot be used to infer the presence of scattered re-emission. Conversely, the presence of emission lines of fluorescent transitions reveals that emission filling cannot be neglected. © 2015. The American Astronomical Society. All rights reserved.

Villalobos A.,University of Groningen | Villalobos A.,National institute for astrophysics | Kazantzidis S.,Ohio State University | Helmi A.,University of Groningen
Astrophysical Journal | Year: 2010

We perform collisionless N-body simulations to investigate the evolution of the structural and kinematical properties of simulated thick disks induced by the growth of an embedded thin disk. The thick disks used in the present study originate from cosmologically common 5:1 encounters between initially thin primary disk galaxies and infalling satellites. The growing thin disks are modeled as static gravitational potentials and we explore a variety of growing-disk parameters that are likely to influence the response of thick disks. We find that the final thick-disk properties depend strongly on the total mass and radial scale length of the growing thin disk, and much less sensitively on its growth timescale and vertical scale height as well as the initial sense of thick-disk rotation. Overall, the growth of an embedded thin disk can cause a substantial contraction in both the radial and vertical direction, resulting in a significant decrease in the scale lengths and scale heights of thick disks. Kinematically, a growing thin disk can induce a notable increase in the mean rotation and velocity dispersions of thick-disk stars. We conclude that the reformation of a thin disk via gas accretion may play a significant role in setting the structure and kinematics of thick disks, and thus it is an important ingredient in models of thick-disk formation. © 2010. The American Astronomical Society. All rights reserved.

La Franca F.,Third University of Rome | Melini G.,Third University of Rome | Fiore F.,National institute for astrophysics
Astrophysical Journal | Year: 2010

We studied the active galactic nucleus (AGN) radio emission from a compilation of hard X-ray-selected samples, all observed in the 1.4 GHz band. A total of more than 1600 AGNs with 2-10 keV de-absorbed luminosities higher than 1042 erg s-1 cm-2 were used. For a sub-sample of about fifty z ≲ 0.1 AGNs, it was possible to reach ∼80% of radio detections and therefore, for the first time, it was possible to almost completely measure the probability distribution function of the ratio between the radio and the X-ray luminosity RX = log(L1.4/LX), where L1.4/LX = vLv(1.4 GHz)/LX(2-10 keV). The probability distribution function of RX was functionally fitted as dependent on the X-ray luminosity and redshift, P(RX\LX,z). It roughly spans over six decades (-7 1022 cm-2) and un-absorbed AGNs. Measurement of the probability distribution function of RX allowed us to compute the kinetic luminosity function and the kinetic energy density which, at variance with that assumed in many galaxy evolution models, is observed to decrease by about a factor of 5 at redshift below 0.5. About half of the kinetic energy density results in being produced by the more radio quiet (RX< -4) AGNs. In agreement with previous estimates, the AGN efficiency ∈kin in converting the accreted mass energy into kinetic power (LK = ∈kin mc2) is, on average, ∈kin-b∼ 5 × 10-3. The data suggest a possible increase of fkin at low redshifts. © 2010. The American Astronomical Society. All rights reserved.

Smart R.L.,National institute for astrophysics | Nicastro L.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Astronomy and Astrophysics | Year: 2014

Aims. We describe the production of the Initial Gaia Source List (IGSL) used both as the starting point for observation-matching in the Gaia data processing and as a comparison catalog to trigger early science alerts. Methods. The IGSL was compiled from large scale public catalogs and a few specific catalogs provided by the Gaia Consortium. For all entries, a Gaia G magnitude is estimated and all objects with a G< 21.0 were included. Results. The catalog has 1222598530 entries with the J2000 ICRF positions, proper motions, classification (star/non-star), and estimates of the Gaia G, Gaia Grvs, Guide Star Catalog red (RF) and blue (BJ) magnitudes. It is available from the Centre de Données astronomiques de Strasbourg. © 2014 ESO.

Ram R.S.,University of York | Brooke J.S.A.,University of York | Bernath P.F.,University of York | Bernath P.F.,Old Dominion University | And 3 more authors.
Astrophysical Journal, Supplement Series | Year: 2014

We present new, accurate predictions for rotational line positions, excitation energies, and transition probabilities of the 12C 13C isotopologue Swan d3Π-a3Π system 0-0, 0-1, 0-2, 1-0, 1-1, 1-2, 2-0, 2-1, and 2-2 vibrational bands. The line positions and energy levels were predicted through new analyses of published laboratory data for the 12C13C lines. Transition probabilities were derived from recent computations of transition dipole moments and related quantities. The 12C13C line data were combined with similar data for 12C2, reported in a companion paper, and applied to produce synthetic spectra of carbon-rich metal-poor stars that have strong C2 Swan bands. The matches between synthesized and observed spectra were used to estimate band head positions for a few of the 12C13C vibrational bands and to verify that the new computed line data match observed spectra. The much weaker C2 lines of the bright red giant Arcturus were also synthesized in the band head regions. © 2014. The American Astronomical Society. All rights reserved.

Bolton J.S.,University of Nottingham | Becker G.D.,Kavli Institute for Cosmology and Institute of Astronomy | Haehnelt M.G.,Kavli Institute for Cosmology and Institute of Astronomy | Viel M.,National institute for astrophysics | Viel M.,National Institute of Nuclear Physics, Italy
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present newmeasurements of the thermal state of the intergalactic medium (IGM) at z̃2.4 derived from absorption line profiles in the Lyα forest. We use a large set of high-resolution hydrodynamical simulations to calibrate the relationship between the temperature-density (T-δ) relation in theIGMand the distribution ofHI column densities,NHI, and velocity widths, bHI, of discrete Lyα forest absorbers. This calibration is then applied to the measurement of the lower cut-off of the bHI-NHI distribution recently presented by Rudie et al. We infer a powerlaw T-δ relation, T = T00δγ-1, with a temperature at mean density, T0 = [1.00+0.32 -0.21] × 104 K and slope (γ-1) = 0.54 ± 0.11. The slope is fully consistent with that advocated by the analysis of Rudie et al.; however, the temperature at mean density is lower by almost a factor of 2, primarily due to an adjustment in the relationship between column density and physical density assumed by these authors. These new results are in excellent agreement with the recent temperature measurements of Becker et al., based on the curvature of the transmitted flux in the Lya forest. This suggests that the thermal state of the IGM at this redshift is reasonably well characterized over the range of densities probed by these methods © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Carbillet M.,University of Nice Sophia Antipolis | Riccardi A.,National institute for astrophysics
Applied Optics | Year: 2010

We present the results of a comparison made between standard charge-coupled devices (CCDs) and lowlight-level (LLL) CCDs in the framework of pyramid wavefront sensing for astronomical adaptive optics (AO) systems on 8 m class telescopes. This comparison is based on detailed end-to-end numerical simulations of the first-light AO system of the Large Binocular Telescope, a relevant example of a pyramid- based AO system. While the model used for simulating the standard CCD is the usual well-established one, mainly based on the consideration of Poisson photon noise and Gaussian readout noise (RON), the model used for the LLLCCD is not only made through the simplistic consideration of a subelectron equivalent RON, but also through the establishment of a gamma distribution. Moreover, an additional dark current component, also resulting from the peculiar architecture of LLLCCDs, is considered. The results obtained clearly show a gain of roughly 0.8 magnitude when considering K-band Strehl ratios ranging from 15% to 60%, at least in the particular case study chosen (Fried parameter characterizing the turbulent atmosphere above the telescope r0 = 15 cm and low light levels). © 2010 Optical Society of America.

De Lucia G.,National institute for astrophysics
Astrophysics and Space Science Proceedings | Year: 2016

In this review I will summarize the status of modern theories of galaxy formation and evolution. I will briefly introduce the main techniques employed and highlight recent successes and open problems. © Springer International Publishing Switzerland 2016.

Andretta V.,National institute for astrophysics | Del Zanna G.,University of Cambridge
Astronomy and Astrophysics | Year: 2014

For the first time, we present and discuss EUV radiances of the solar transition region (TR) and corona obtained during a solar cycle. The measurements were obtained with the SOHO/coronal diagnostic spectrometer (CDS) during the period from 1996 to 2010. We find that limb-brightening significantly affects any characterisation of the solar radiances. We present the limb-brightening function for the main lines and find that it does not change measurably during the cycle. We confirm earlier findings that the radiance histogram of the cooler lines have a well defined, log-normal quiet-Sun component, although our results differ from previous ones. The width of the lowest-radiance log-normal distribution is constant along the cycle. Both the analysis of the centre-to-limb variation and of the radiance statistical distribution point to a constant quiet Sun emission along solar cycle 23. Lines formed above 1 MK are dramatically affected by the presence of active regions, and indeed, no "quiet Sun" region can be defined during periods of maximum activity. Much of the irradiance variability in lines formed below 1.5 MK is due to a change in the emitting area. For hotter lines, the emitting area saturates to almost 100% of full solar disk at the maximum of activity, while simultaneously the emission due to active regions increases by more than an order of magnitude. We show that structures around active regions, sometimes referred to as dark halos or dark canopies, are common and discuss their similarities and differences with coronal holes. In particular, we show how they are well visible in TR lines, contrary to coronal holes. © ESO, 2014.

Massi M.,Max Planck Institute for Radio Astronomy | Torricelli-Ciamponi G.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2014

Aims. Our aim is to show how variable Doppler boosting of an intrinsically variable jet can explain the long-term modulation of 1667 ± 8 days observed in the radio emission of LS I +61°303. Methods. The physical scenario is that of a conical, magnetized plasma jet having a periodical (P 1) increase of relativistic particles, Nrel, at a specific orbital phase, as predicted by accretion in the eccentric orbit of LS I +61°303. Jet precession (P2) changes the angle, η, between jet axis and line of sight, thereby inducing variable Doppler boosting. The problem is defined in spherical geometry, and the optical depth through the precessing jet is calculated by taking into account that the plasma is stratified along the jet axis. The synchrotron emission of such a jet was calculated and we fitted the resulting flux density Smodel(t) to the observed flux density obtained during a 6.5-year monitoring of LS I +61°303 by the Green Bank radio interferometer. Results. Our physical model for the system LS I +61°303 is not only able to reproduce the long-term modulation in the radio emission, but it also reproduces all the other observed characteristics of the radio source, the orbital modulation of the outbursts, their orbital phase shift, and their spectral index properties. Moreover, a correspondence seems to exist between variations in the ejection angle induced by precession and the rapid rotation in position angle observed in VLBA images. Conclusions. The peak of the long-term modulation occurs when the jet electron density is around its maximum and the approaching jet is forming the smallest possible angle with the line of sight. This coincidence of maximum number of emitting particles and maximum Doppler boosting of their emission occurs every ~1667 days and creates the long-term modulation observed in LS I +61°303. © ESO, 2014.

Markovic K.,Ludwig Maximilians University of Munich | Viel M.,National institute for astrophysics | Viel M.,National Institute of Nuclear Physics, Italy
Publications of the Astronomical Society of Australia | Year: 2014

We review the current state of the theory of large-scale structure in a warm dark matter (WDM) cosmological model. In particular, we focus on the non-linear modelling of the matter power spectrum and on the mass function of dark matter haloes. We describe the results of N-body simulations with WDM and mention the effects that could be induced by baryonic physics. We also examine the halo model of large-scale structure and its recently suggested modifications for a WDM cosmology, which account for the small-scale smoothness of the initial matter density field and better fit the results of N-body simulations. Having described the theoretical models, we discuss the current lower limits on the WDM particle mass, m wdm, which correspond to upper limits on the WDM temperature under the assumption that the particles are thermal relics. The best such constraints come from the Lyα forest and exclude all masses below 3.3 keV at the 2σ confidence level. We finally review the forecasts for future lensing surveys, which will be of the same order of magnitude as the already existing constraints from the Lyα forest data but explore a different redshift regime. © 2014 Astronomical Society of Australia.

De Marchi G.,European Space Agency | Panagia N.,US Space Telescope Science Institute | Panagia N.,National institute for astrophysics | Panagia N.,Supernova Ltd
Monthly Notices of the Royal Astronomical Society | Year: 2014

We have studied the interstellar extinction in a field of ~3 arcmin × 3 arcmin at the core of the 30 Doradus nebula, including the central R 136 cluster, in the Large Magellanic Cloud. Observations at optical and near-infrared wavelengths, obtained with the WFC 3 camera on board the Hubble Space Telescope, show that the stars belonging to the red giant clump are spread across the colour-magnitude diagrams because of the considerable and uneven levels of extinction in this region. Since these stars share very similar physical properties and are all at the same distance, they allow us to derive the absolute extinction in a straightforward and reliable way. Thus, we have measured the extinction towards about 180 objects and the extinction law in the range 0.3-1.6 μm. At optical wavelengths, the extinction curve is almost parallel to that of the diffuse Galactic interstellar medium. Taking the latter as a template, the value of RV = 4.5 ± 0.2 that we measure indicates that in the optical there is an extra grey component due to a larger fraction of large grains. At wavelengths longer than ~1 μm, the contribution of this additional component tapers off as λ -1.5, like in the MilkyWay, suggesting that the nature of the grains is otherwise similar to those in our Galaxy, but with a ~2.2 times higher fraction of large grains. These results are consistent with the addition of 'fresh' large grains by supernova explosions, as recently revealed by Herschel and ALMA (Atacama Large Millimeter Array) observations of SN 1987A. © 2014 The Authors.

Cappellaro E.,National institute for astrophysics
Astrophysics and Space Science Proceedings | Year: 2016

I review the use of SN Ia as distance indicators for measuring H0, the Hubble constant, and the expansion history of the Universe. Most current estimates of H0 are in the range 74–76km s-1Mpc-1, in significant disagreement with the PLANCK’s CMB estimate that is 10% smaller. The main issues for SN Ia calibration, namely the luminosity vs. light curve shape relation and the correction for dust extinction are briefly addressed. SN Ia have been the key for the discovery of the acceleration of the cosmic expansion and in the near future they are expected to give a significant contribution to reveal the nature of dark energy. © Springer International Publishing Switzerland 2016.

de Martino D.,National institute for astrophysics
Astrophysics and Space Science Proceedings | Year: 2016

Among hard X-ray sources detected in the INTEGRAL/IBIS and Swift/BAT surveys, those identified as accreting white dwarf binaries recently boosted in number, representing ~20% of the Galactic sample. The majority are identified as Cataclysmic Variables with magnetic white dwarf primaries suggesting that this subclass could be an important costituent of the galactic population of X-ray sources. In this paper I present the results of an on-going follow-up progamme in the X-rays aiming at identifying the true nature of newly discovered sources. © Springer International Publishing Switzerland 2016.

Urpin V.,National institute for astrophysics | Urpin V.,RAS Ioffe Physical - Technical Institute
Astronomy and Astrophysics | Year: 2014

Context. Magnetohydrodynamic (MHD) instabilities can play an important role in the dynamics of the pulsar magnetosphere and can be responsible for the formation of various structures. Aims. We consider the instability caused by a gradient of the magnetic pressure, which can occur in a non-neutral magnetospheric plasma of the pulsars. Methods. Stability is discussed by means of a linear analysis of the force-free MHD equations. Results. We argue that the pulsar magnetospheres are always unstable. The unstable disturbances have a form of filaments directed along the magnetic field lines with plasma motions being almost parallel (or anti-parallel) to the magnetic field. The growth rate of instability is high and can reach a fraction of ck, where k is the wavevector of unstable disturbances. The instability can be responsible for fluctuations of plasma and the short-term variability of pulsar emission. © ESO, 2014.

Cassisi S.,National institute for astrophysics | Salaris M.,Liverpool John Moores University
Astronomy and Astrophysics | Year: 2014

A new scenario - early disc accretion - has been proposed very recently to explain the origin of the multiple population phenomenon in Galactic globular clusters. It envisages the possibility that a fraction of low- and very low-mass cluster stars may accrete the ejecta of interacting massive binary (and possibly also fast rotating massive) stars during the fully convective, pre-main sequence stage, to reproduce the CN and ONa anticorrelations observed among stars in individual clusters. This scenario is assumed to be able to explain the presence (and properties) of the multiple populations in the majority of globular clusters in the Milky Way. Here we have considered the well studied cluster NGC 2808, which displays a triple main sequence with well defined and separate He abundances. Knowledge of these abundances allowed us to put strong constraints on the He mass fraction and amount of matter to be accreted by low-mass pre-main sequence stars. We find that the minimum He mass fraction in the accreted gas has to be ~0.44 to produce the observed sequences and that at fixed initial mass of the accreting star, different efficiencies for the accretion are required to produce stars placed onto the multiple main sequences. This may be explained by differences in the orbital properties of the progenitors and/or different spatial distribution of intracluster gas with varying He abundances. Both O-Na and C-N anticorrelations appear naturally along the main sequences, once considering the predicted relationship between He and CNONa abundances in the ejecta of the polluters. As a consequence of the accretion, we predict no discontinuity between the abundance ranges covered by intermediate and blue main sequence stars, but we find a sizeable (several 0.1 dex) discontinuity of the N and Na abundances between objects on the intermediate and red main sequences. There is in principle enough polluting gas with the right He abundances to explain the observed main sequences by early accretion (hence no need to invoke a much higher cluster mass at birth, as required by scenarios envisaging multiple star formation bursts), however the matter ejected by the polluters must not be fully mixed before being accreted otherwise, according to the models, the average He abundance of the polluting gas is too low to produce the observed multiple main sequences. © ESO, 2014.

Munari E.,University of Trieste | Biviano A.,National institute for astrophysics | Biviano A.,CNRS Paris Institute of Astrophysics | Mamon G.A.,CNRS Paris Institute of Astrophysics
Astronomy and Astrophysics | Year: 2014

Aims. We aim to compute the mass and velocity anisotropy profiles of Abell 2142 and, from there, the pseudo phase-space density profile Q(r) and the density slope-velocity anisotropy β-γ relation, and then to compare them with theoretical expectations. Methods. The mass profiles were obtained by using three techniques based on member galaxy kinematics, namely the caustic method, the method of dispersion-kurtosis, and MAMPOSSt. Through the inversion of the Jeans equation, it was possible to compute the velocity anisotropy profiles. Results. The mass profiles, as well as the virial values of mass and radius, computed with the different techniques agree with one another and with the estimates coming from X-ray and weak lensing studies. A combined mass profile is obtained by averaging the lensing, X-ray, and kinematics determinations. The cluster mass profile is well fitted by an NFW profile with c = 4.0 ± 0.5. The population of red and blue galaxies appear to have a different velocity anisotropy configuration, since red galaxies are almost isotropic, while blue galaxies are radially anisotropic, with a weak dependence on radius. The Q(r) profile for the red galaxy population agrees with the theoretical results found in cosmological simulations, suggesting that any bias, relative to the dark matter particles, in velocity dispersion of the red component is independent of radius. The β-γ relation for red galaxies matches the theoretical relation only in the inner region. The deviations might be due to the use of galaxies as tracers of the gravitational potential, unlike the non-collisional tracer used in the theoretical relation. © 2014 ESO.

Fu L.,National institute for astrophysics | Fu L.,Shanghai Normal University | Kilbinger M.,CNRS Paris Institute of Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

The decomposition of the cosmic shear field into E and B mode is an important diagnostic in weak gravitational lensing. However, commonly used techniques to perform this separation suffer from mode-mixing on very small or very large scales. We introduce a new E-/B-mode decomposition of the cosmic shear two-point correlation on a finite interval. This new statistic is optimized for cosmological applications, by maximizing the signal-to-noise ratio (S/N) and a figure of merit (FoM) based on the Fisher matrix of the cosmological parameters Ωm and σ8. We improve both S/N and FoM results substantially with respect to the recently introduced ring statistic, which also provides E-/B-mode separation on a finite angular range. The S/N (FoM) is larger by a factor of 3 (2) on angular scales between 1 and 220 arcmin. In addition, it yields better results than for the aperture-mass dispersion 〈M2ap〉, with improvements of 20 per cent (10 per cent) for S/N (FoM). Our results depend on the survey parameters, most importantly on the covariance of the two-point shear correlation function. Although we assume parameters according to the CFHTLS-Wide survey, our method and optimization scheme can be applied easily to any given survey settings and observing parameters. Arbitrary quantities, with respect to which the E-/B-mode filter is optimized, can be defined, therefore generalizing the aim and context of the new shear statistic. © 2009 RAS.

Tenorio-Tagle G.,National Institute of Astrophysics, Optics and Electronics | Munoz-Tunon C.,Institute of Astrophysics of Canarias | Silich S.,National Institute of Astrophysics, Optics and Electronics | Cassisi S.,National institute for astrophysics
Astrophysical Journal Letters | Year: 2015

Our arguments deal with the early evolution of Galactic globular clusters and show why only a few of the supernovae (SNe) products were retained within globular clusters and only in the most massive cases (M ≥ 106 Mo), while less massive clusters were not contaminated at all by SNe. Here, we show that SN blast waves evolving in a steep density gradient undergo blowout and end up discharging their energy and metals into the medium surrounding the clusters. This inhibits the dispersal and the contamination of the gas left over from a first stellar generation. Only the ejecta from well-centered SNe that evolve into a high-density medium available for a second stellar generation (2SG) in the most massive clusters would be retained. These are likely to mix their products with the remaining gas, eventually leading in these cases to an Fe-contaminated 2SG. © 2015. The American Astronomical Society. All rights reserved.

Damiani A.,University of Santiago de Chile | De Simone S.,CNR Institute of Neuroscience | Rafanelli C.,CNR Institute of Neuroscience | Cordero R.R.,University of Santiago de Chile | Laurenza M.,National institute for astrophysics
Remote Sensing of Environment | Year: 2012

Continuous ground-based total ozone measurements were carried out at Ny-Ålesund (78.9°N, 11.9° E, Svalbard islands, Norway), by using a Brewer spectrophotometer, for almost three years (2007-2009). Given the scarcity of high-quality ground-based measurements performed at high latitudes, this dataset provides a rare opportunity to check the quality of satellite-based data recorded in Arctic. Considering the unprecedented Artic ozone loss recently derived from satellite observations, assessing the reliability of satellite readings at such high latitudes is a timely effort. This study focuses on the comparisons between ground-based Brewer total ozone measurements and satellite ozone readings retrieved from EOS Aura Ozone Measurement Instrument (OMI) (by using OMI-TOMS and OMI-DOAS algorithms), retrieved from ERS-2 Global Ozone Monitoring Experiment (GOME) (by using TOGOMI algorithm) and from Envisat SCanning Imaging Absorption spectrometer for Atmospheric CartographY (SCIAMACHY) (by using TOSOMI algorithm).Despite the extreme conditions that affect both ground- and satellite-based measurements, a good agreement was found (r= 0.99 for OMI-TOMS, r= 0.97 for both OMI-DOAS and GOME datasets and r= 0.96 for SCIAMACHY). Nevertheless, space-based total ozone readings were found to underestimate ground-based data, in agreement with prior results. OMI-TOMS data showed the highest negative mean bias (MB=-2.03%) whereas DOAS-based datasets showed a better agreement (MB=-0.47, -0.69 and -0.01% for OMI-DOAS, GOME and SCIAMACHY, respectively) but a greater data scatter. On the other hand, DOAS-based datasets present an important seasonal dependence; an overestimation of the Brewer total ozone up to about 3% is found in April and September with respect to OMI-DOAS and SCIAMACHY while in September with respect to GOME. In contrast, differences between OMI-TOMS and Brewer total ozone do not present significant dependence on the season or on geometrical parameters (i.e., satellite solar and viewing zenith angles). Differences in total ozone values between ground-based and satellite measurements are further discussed attending to the algorithm differences in dealing with cloud cover under high surface albedo (i.e., snow) conditions.Extending the study to Sodankyla station (67.3°N, 26.6°E, Finland), similarities and differences between the two stations have been highlighted. The agreement between satellite and Brewer data slightly improved when Sodankyla station is considered. On the continent, the seasonal dependence and data scatter for DOAS-based datasets and the MB for OMI-TOMS are smaller with respect to Ny-Ålesund. Moreover, the roughly constant ozone summer offset (about 1%) between OMI-TOMS and OMI-DOAS, well evident for Ny-Ålesund, is not present for Sodankyla. Finally, some patterns in the geographic distributions of the satellite-Brewer total ozone differences are evident only for Ny-Ålesund, partly because of the peculiar characteristics of the surface albedo (higher than in Sodankyla, with a strong water/land contrast). © 2012 Elsevier Inc.

Moscadelli L.,National institute for astrophysics | Xu Y.,Chinese Academy of Sciences | Chen X.,Chinese Academy of Sciences
Astrophysical Journal | Year: 2010

We derive accurate proper motions of the CH3OH 12GHz masers toward the W3(OH) ultra-compact (UC) H II region, employing seven epochs of VLBA observations spanning a time interval of about 10 yr. The achieved velocity accuracy is of the order of 0.1kms-1, adequate to precisely measure the relative velocities of most of the 12GHz masers in W3(OH), with amplitude varying in the range 0.3-3kms-1. Toward W3(OH), the most intense 12GHz masers concentrate in a small area toward the north (the northern clump) of the UC H II region. We have compared the proper motions of the CH 3OH 12GHz masers with those (derived from literature data) of the OH 6035 MHz masers, emitting from the same region of the methanol masers. In the northern clump, the two maser emissions emerge from nearby (but likely distinct) cloudlets of masing gas with, in general, a rather smooth variation of line-of-sight and sky-projected velocities, which suggests some connection of the environments and kinematics traced by both maser types. The conical outflow model, previously proposed to account for the 12GHz maser kinematics in the northern clump, does not reproduce the new, accurate measurements of 12GHz maser proper motions and has to be rejected. We focus on the subset of 12GHz masers of the northern clump belonging to the "linear structure at P.A. = 130°-140°," whose regular variation of LSR velocities with position presents evidence for some ordered motion. We show that the three-dimensional velocities of this "linear distribution" of 12GHz masers can be well fitted considering a flat, rotating disk, seen almost edge-on. © 2010. The American Astronomical Society.

Turrini D.,National institute for astrophysics | Nelson R.P.,Queen Mary, University of London | Barbieri M.,University of Padua
Experimental Astronomy | Year: 2015

Over the last twenty years, the search for extrasolar planets has revealed the rich diversity of outcomes from the formation and evolution of planetary systems. In order to fully understand how these extrasolar planets came to be, however, the orbital and physical data we possess are not enough, and they need to be complemented with information about the composition of the exoplanets. Ground-based and space-based observations provided the first data on the atmospheric composition of a few extrasolar planets, but a larger and more detailed sample is required before we can fully take advantage of it. The primary goal of a dedicated space mission like the Exoplanet Characterization Observatory (EChO) proposal is to fill this gap and to expand the limited data we possess by performing a systematic survey of extrasolar planets. The full exploitation of the data that space-based and ground-based facilities will provide in the near future, however, requires knowledge about the sources and sinks of the chemical species and molecules that will be observed. Luckily, the study of the past history of the Solar System provides several indications about the effects of processes like migration, late accretion and secular impacts, and on the time they occur in the life of planetary systems. In this work we will review what is already known about the factors influencing the composition of planetary atmospheres, focusing on the case of gaseous giant planets, and what instead still need to be investigated. © 2014, The Author(s).

Micela G.,National institute for astrophysics
Experimental Astronomy | Year: 2015

Stellar activity is the major astrophysical limiting factor for the study of planetary atmospheres. Its variability and spectral characteristics may affect the extraction of the planetary signal even for moderately active stars. A technique based on spectral change in the visible band was developed to estimate the effects in the infrared due to star activity. This method has been purposely developed for the EChO mission which had the crucial characteristics of monitoring simultaneously a broadband from visible to infrared. Thanks to this capability the optical spectrum, whose variations are mainly due to stellar activity, has been used as in an instantaneous calibrator to correct the infrared spectrum. The technique is based on principal component analysis which significantly reduces the dimensionality of the spectra. The method was tested on a set of simulations with realistic photon noise. It can be generalized to any chromatic variability effects provided that optical and infrared variations are correlated. © 2014, Springer Science+Business Media Dordrecht.

Morlino G.,National institute for astrophysics
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2013

We review the basic features of particle acceleration theory around collisionless shocks in supernova remnants (SNRs). We show how non-linear effects induced by the back reaction of accelerated particles onto the shock dynamics are of paramount importance to support the hipotesys that SNRs are the factories of Galactic cosmic rays. Recent developments in the modeling of the mechanism of diffusive shock acceleration are discussed, with emphasis on the role of magnetic field amplification and the presence of neutrals in the circumstellar environment. Special attention will be devoted to observational consequences of non-linear effects on the multi-wavelength spectrum of SNRs, with emphasis on X-ray and gamma-ray emission. Finally we also discuss how Balmer lines, detected from several young SNRs, can be used to estimate the shock dynamical properties and the efficiency of CR acceleration. © 2012 Elsevier B.V.

Spiga D.,National institute for astrophysics | Raimondi L.,Elettra - Sincrotrone Trieste | Svetina C.,Elettra - Sincrotrone Trieste | Zangrando M.,Elettra - Sincrotrone Trieste | Zangrando M.,CNR Institute of Materials
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2013

X-ray mirrors with high focusing performances are in use in both mirror modules for X-ray telescopes and in synchrotron and FEL (Free Electron Laser) beamlines. A degradation of the focus sharpness arises in general from geometrical deformations and surface roughness, the former usually described by geometrical optics and the latter by physical optics. In general, technological developments are aimed at a very tight focusing, which requires the mirror profile to comply with the nominal shape as much as possible and to keep the roughness at a negligible level. However, a deliberate deformation of the mirror can be made to endow the focus with a desired size and distribution, via piezo actuators as done at the EIS-TIMEX beamline of FERMI@Elettra. The resulting profile can be characterized with a Long Trace Profilometer and correlated with the expected optical quality via a wavefront propagation code. However, if the roughness contribution can be neglected, the computation can be performed via a raytracing routine, and, under opportune assumptions, the focal spot profile (the Point Spread Function, PSF) can even be predicted analytically. The advantage of this approach is that the analytical relation can be reversed; i.e., from the desired PSF the required mirror profile can be computed easily, thereby avoiding the use of complex and time-consuming numerical codes. The method can also be suited in the case of spatially inhomogeneous beam intensities, as commonly experienced at synchrotrons and FELs. In this work we expose the analytical method and the application to the beam shaping problem. © 2012 Elsevier B.V. All rights reserved.

Blakeslee J.P.,National Research Council Canada | Cantiello M.,National institute for astrophysics | Peng E.W.,Peking University | Peng E.W.,Kavli Institute for Astronomy and Astrophysics
Astrophysical Journal | Year: 2010

Two recent empirical developments in the study of extragalactic globular cluster (GC) populations are the color-magnitude relation of the blue GCs (the "blue tilt") and the nonlinearity of the dependence of optical GC colors on metallicity. The color-magnitude relation, interpreted as a mass-metallicity relation, is thought to be a consequence of self-enrichment. Nonlinear color-metallicity relations have been shown to produce bimodal color distributions from unimodal metallicity distributions. We simulate GC populations including both a mass-metallicity scaling relation and nonlinear color-metallicity relations motivated by theory and observations. Depending on the assumed range of metallicities and the width of the GC luminosity function (GCLF), we find that the simulated populations can have bimodal color distributions with a "blue tilt" similar to observations, even though the metallicity distribution appears unimodal. The models that produce these features have the relatively high mean GC metallicities and nearly equal blue and red peaks characteristic of giant elliptical galaxies. The blue tilt is less apparent in the models with metallicities typical of dwarf ellipticals; the narrower GCLF in these galaxies has an even bigger effect in reducing the significance of their color-magnitude slopes. We critically examine the evidence for nonlinearity versus bimodal metallicities as explanations for the characteristic double-peaked color histograms of giant ellipticals and conclude that the question remains open. We discuss the prospects for further theoretical and observational progress in constraining the models presented here and for uncovering the true metallicity distributions of extragalactic GC systems. © 2010. The American Astronomical Society. All rights reserved..

Poletto G.,National institute for astrophysics
Living Reviews in Solar Physics | Year: 2015

Polar plumes are thin long ray-like structures that project beyond the limb of the Sun polar regions, maintaining their identity over distances of several solar radii. Plumes have been first observed in white-light (WL) images of the Sun, but, with the advent of the space era, they have been identified also in X-ray and UV wavelengths (XUV) and, possibly, even in in situ data. This review traces the history of plumes, from the time they have been first imaged, to the complex means by which nowadays we attempt to reconstruct their 3-D structure. Spectroscopic techniques allowed us also to infer the physical parameters of plumes and estimate their electron and kinetic temperatures and their densities. However, perhaps the most interesting problem we need to solve is the role they cover in the solar wind origin and acceleration: Does the solar wind emanate from plumes or from the ambient coronal hole wherein they are embedded? Do plumes have a role in solar wind acceleration and mass loading? Answers to these questions are still somewhat ambiguous and theoretical modeling does not provide definite answers either. Recent data, with an unprecedented high spatial and temporal resolution, provide new information on the fine structure of plumes, their temporal evolution and relationship with other transient phenomena that may shed further light on these elusive features. © The Author(s).

Salaris M.,Liverpool John Moores University | Cassisi S.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2014

A new scenario - early disc accretion - has recently been proposed to explain the discovery of multiple stellar populations in Galactic globular clusters. According to this model, the existence of well defined (anti-)correlations amongst light element abundances (i.e. C, N, O, Na) in the photospheres of stars belonging to the same cluster (and the associated helium enrichment) is caused by accretion of the ejecta of short-lived interacting massive binary systems (and single fast rotating massive stars) on fully convective pre-main sequence low- and very low-mass stars, during the early stages of the cluster evolution. In a previous paper we applied this scenario to the cluster NGC 2808, showing how the knowledge of the He abundance of its triple main sequence can constrain both the He abundance of the accreted matter and the accretion efficiency. Here we have investigated the constraints provided by considering simultaneously the observed spread of lithium and oxygen (and when possible also sodium) abundances for samples of turn-off stars in NGC 6752, NGC 6121 (M4), and NGC 104 (47Tuc), and the helium abundance of their multiple main sequences. These observations provide a very powerful test of the accretion scenario, because the observed O, Li, and He abundance distributions at the turn-off can be used to constrain the composition (and mass) of the accreted matter and the timescales of the polluting stars. In the case of NGC 6752, we could not find a physically consistent solution. If early disc accretion does happen, observations point towards accretion of gas with a non-negligible Li abundance, contrary to the expectations for the ejecta of the "natural" polluters in this scenario. For M4, spectroscopic errors are too large compared to the intrinsic spread, to constrain the properties of the accreted matter. As for 47Tuc, we could find a physically consistent solution for the abundances of He and O (and Na) in the accreted gas and predict the abundances of these elements in the accreted matter - that will have to be reproduced by evolutionary calculations for the polluters and simulations of the global evolution of the intracluster gas - only if pollution happens with timescales of ∼1 Myr, so polluters are objects with masses of several tens of solar masses. Accurate spectroscopic measurements of Li and other light elements in dwarf stars in a larger sample of clusters are needed to test this scenario more comprehensively. © 2014 ESO.

Moscadelli L.,National institute for astrophysics | Goddi C.,Joint Institute for VLBI in Europe
Astronomy and Astrophysics | Year: 2014

Context. It has been claimed that NGC 7538 IRS1 is a high-mass young stellar object (YSO) with 30 M⊙, surrounded by a rotating Keplerian disk, probed by a linear distribution of methanol masers. The YSO is also powering a strong compact Hii region or ionized wind, and is driving at least one molecular outflow. The axis orientations of the different structures (ionized gas, outflow, and disk) are, however, misaligned, which has led to the different competing models proposed to explain individual structures. Aims. We investigate the 3D kinematics and dynamics of circumstellar gas with very high linear resolution, from tens to 1500 AU, with the ultimate goal of building a comprehensive dynamical model for what is considered the best high-mass accretion disk candidate around an O-type young star in the northern hemisphere. Methods. We used high-angular resolution observations of 6.7 GHz CH 3OH masers with the EVN, NH3 inversion lines with the JVLA B-Array, and radio continuum with the VLA A-Array. In particular, we employed four different observing epochs of EVN data at 6.7 GHz, spanning almost eight years, which enabled us to measure line-of-sight (l.o.s.) accelerations and proper motions of CH3OH masers, besides l.o.s. velocities and positions (as done in previous works). In addition, we imaged highly excited NH3 inversion lines, from (6,6) to (13,13), which enabled us to probe the hottest molecular gas very close to the exciting source(s). Results. We confirm previous results that five 6.7 GHz maser clusters (labeled from "A" to "E") are distributed over a region extended N-S across ≈ 1500 AU, and are associated with three components of the radio continuum emission. We propose that these maser clusters identify three individual high-mass YSOs in NGC 7538 IRS1, named IRS1a (associated with clusters "B" and "C"), IRS1b (associated with cluster "A"), and IRS1c (associated with cluster "E"). We find that the 6.7 GHz masers distribute along a line, with a regular variation in V LSR with position, along the major axis of the distribution of maser cluster "A" and the combined clusters "B" + "C". A similar VLSR gradient (although shallower) is also detected in the NH3 inversion lines. Interestingly, the variation in VLSR with projected position is not linear but quadratic for both maser clusters. We measure proper motions for 33 maser features, which have an average amplitude (4.8 ± 0.6 km s-1) similar to the variation in VLSR across the maser cluster, and are approximately parallel to the clusters' elongation axes. By studying the time variation in the maser spectrum, we also derive l.o.s. accelerations for 30 features, with typical amplitude of ~ 10 -3-10-2 km s-1 yr-1. We modeled the masers in both clusters "A" and "B" + "C" in terms of an edge-on disk in centrifugal equilibrium. Based on our modeling, masers of clusters "B" + "C" may trace a quasi-Keplerian ∼1 M⊙, thin disk, orbiting around a high-mass YSO, IRS1a, of up to ≈ 25 M⊙. This YSO dominates the bolometric luminosity of the region. The disk traced by the masers of cluster "A" is both massive (≲ 16 M⊙ inside a radius of ≈ 500 AU) and thick (opening angle ≈ 45°), and the mass of the central YSO, IRS1b, is constrained to be at most a few M⊙. Towards cluster "E", NH 3 and 6.7 GHz masers trace more quiescent dynamics than for the other clusters. The presence of a radio continuum peak suggests that the YSO associated with the cluster "E", IRS1c, may be an ionizing, massive YSO as well. Conclusions. We present compelling evidence that NGC 7538 IRS1 is forming not just one single high-mass YSO, but consists of a multiple system of high-mass YSOs, which are surrounded by accretion disks and are probably driving individual outflows. This new model naturally explains all the different orientations and disk/outflow structures proposed for the region in previous models. © 2014 ESO.

Stangalini M.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2014

A recent study carried out on high-sensitivity SUNRISE/IMAX data has reported about areas of limited flux emergence in the quiet Sun. By exploiting an independent and longer (four hours) data set acquired by Hinode/SOT, we investigate these regions in more detail by analysing their spatial distribution and relation with the supergranular flow. Our findings, while confirming these calm areas, also show that the emergence rate of small magnetic elements is largely suppressed at the locations where the divergence of the supergranular plasma flows is positive. This means that the dead-calm areas previously reported in literature are not randomly distributed across the solar photosphere, but are linked to the supergranular cells themselves. These results are discussed in the framework of the recent literature. © 2014 ESO.

Lanza A.F.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2014

Aims. The chromospheric emission of stars with close-in transiting planets has been found to correlate with the surface gravity of their planets. Stars with low-gravity planets have on average a lower chromospheric flux. Methods. We propose that this correlation is due to the absorption by circumstellar matter that comes from the evaporation of the planets. Planets with a lower gravity have a greater mass-loss rate, which leads to a higher column density of circumstellar absorption and in turn explains the lower level of chromospheric emission observed in their host stars. We estimated the required column density and found that planetary evaporation can account for it. We derived a theoretical relationship between the chromospheric emission as measured in the core of the Ca II H&K lines and the planet gravity. Results. We applied this relationship to a sample of transiting systems for which both the stellar Ca II H&K emission and the planetary surface gravity are known and found a good agreement, given the various sources of uncertainties and the intrinsic variability of the stellar emissions and planetary evaporation rates. We consider implications for the radial velocity jitter applied to fit the spectroscopic orbits and for the age estimates of planetary systems based on the chromospheric activity level of their host stars. © ESO, 2014.

Musella I.,National institute for astrophysics
Astrophysics and Space Science Proceedings | Year: 2016

Classical Cepheids plays a key role in the calibration of the extragalactic distance scale. In spite of their importance, some uncertainties related to their properties remain. In particular, a general consensus on the possible dependence on the metallicity of the host galaxy of the Cepheid properties has not been reached yet. These uncertainties could produce significant systematic errors in the calibration of the secondary distance indicators we need to reach cosmologically significant distances and in turn in the evaluation of the Hubble constant H0. Possible solutions are discussed. © Springer International Publishing Switzerland 2016.

Bonanno A.,National institute for astrophysics | Bonanno A.,National Institute of Nuclear Physics, Italy | Zappala D.,National Institute of Nuclear Physics, Italy
Nuclear Physics B | Year: 2015

The Lifshitz critical behavior for a single component field theory is studied for the specific isotropic case in the framework of the Functional Renormalization Group. Lifshitz fixed point solutions of the flow equation, derived by using a Proper Time regulator, are searched at lowest and higher order in the derivative expansion. Solutions are found when the number of spatial dimensions d is contained within the interval 5.5. < d < 8. © 2015 The Authors.

Schneider R.,National institute for astrophysics | Omukai K.,Japan National Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2010

We investigate the effects of the cosmic microwave background (CMB) radiation field on the collapse of pre-stellar clouds. Using a semi-analytic model to follow the thermal evolution of clouds with varying initial metallicities and dust contents at different redshifts, we study self-consistently the response of the mean Jeans mass at cloud fragmentation to metal line cooling, dust cooling and the CMB.In the absence of dust grains, at redshifts z ≤ 10 moderate characteristic masses (of tens of M. ⊙) are formed when the metallicity is 10-4 Z⊙ ≤ Z ≤ 10-2.5 Z⊙; at higher metallicities, the CMB inhibits fragmentation and only very large masses (of approximately hundreds of M. ⊙) are formed. These effects become even more dramatic at z > 10 and the fragmentation mass scales are always ≥hundreds of M. ⊙, independent of the initial metallicity.When dust grains are present, sub-solar mass fragments are formed at any redshift for metallicities Z ≥ 10-6 Z⊙ because dust cooling remains relatively insensitive to the presence of the CMB. When Z > 10-3 Z⊙, heating of dust grains by the CMB at z ≥ 5 favours the formation of larger masses, which become super-solar when Z ≥ 10-2 Z⊙ and z ≥ 10. Finally, we discuss the implications of our result for the interpretation of the observed abundance patterns of very metal-poor stars in the Galactic halo. © 2009 The Authors. Journal compilation © 2009 RAS.

Tavecchio F.,National institute for astrophysics | Roncadelli M.,National Institute of Nuclear Physics, Italy | Galanti G.,University of Insubria
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

The idea that photons can convert to axion-like particles (ALPs) γ→. a in or around an AGN and reconvert back to photons a→γ in the Milky Way magnetic field has been put forward in 2008 and has recently attracted growing interest. Yet, so far nobody has estimated the conversion probability γ→. a as carefully as allowed by present-day knowledge. Our aim is to fill this gap. We first remark that AGN which can be detected above 100 GeV are blazars, namely AGN with jets, with one of them pointing towards us. Moreover, blazars fall into two well defined classes: BL Lac objects (BL Lacs) and Flat Spectrum Radio Quasars (FSRQs), with drastically different properties. In this Letter we report a preliminary evaluation of the γ→. a conversion probability inside these two classes of blazars. Our findings are surprising. Indeed, while in the case of BL Lacs the conversion probability turns out to be totally unpredictable due to the strong dependence on the values of the somewhat uncertain position of the emission region along the jet and strength of the magnetic field therein, for FSRQs we are able to make a clear-cut prediction. Our results are of paramount importance in view of the planned very-high-energy photon detectors like the CTA, HAWK, GAMMA-400 and HISCORE. © 2015 The Authors.

Villata M.,National institute for astrophysics
Annalen der Physik | Year: 2015

Repulsive gravity is not very popular in physics. However, one comes across it in at least two main occurrences in general relativity: in the negative-r region of Kerr spacetime, and as the result of the gravitational interaction between matter and antimatter, when the latter is assumed to be CPT-transformed matter. Here we show how these two independent developments of general relativity are perfectly consistent in predicting gravitational repulsion and how the above Kerr negative-r region can be interpreted as the habitat of antimatter. As a consequence, matter particles traveling along vortical geodesics can pass through the throat of a rotating black hole and emerge as antimatter particles (and vice versa). An experimental definitive answer on the gravitational behavior of antimatter is awaited in the next few years. © 2015 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Claudi R.,National institute for astrophysics
Astrophysics and Space Science | Year: 2010

The satellite PLATO represents a new challenge for future investigations of exoplanets and oscillations of stars. It is one of the proposed missions of ESA COSMIC VISION 2015-2025 and it is scheduled for launch in 2017. The goal of the mission is a full characterization of the planet star systems with an asteroseismic analysis of the host stars. The PLATO Payload Consortium (PPLC) includes several European countries which are employed in the assessment study of the mission. Thanks to the high precision photometry, PLATO is thought to be able to detect planets and oscillations within a large sample of targets. © 2010 Springer Science+Business Media B.V.

Valenti E.,European Southern Observatory | Valenti E.,University of Chile | Ferraro F.R.,University of Bologna | Origlia L.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present near-infrared colour-magnitude diagrams and physical parameters for a sample of 12 galactic globular clusters located towards the inner bulge region. For each cluster we provide measurements of the reddening, distance and photometric metallicity and of the luminosity of the horizontal branch red clump and the red giant branch bump and tip. The sample discussed here, together with that presented in Valenti, Ferraro & Origlia (2007), represents the largest homogeneous catalogue of bulge globular clusters (comprising ∼80 per cent of the entire bulge cluster population) ever studied.The compilation is available in electronic form on the World Wide Web (http://www.bo.astro.it/~GC/ir_archive). © 2009 The Authors. Journal compilation © 2009 RAS.

Blasi P.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

We discuss a semi-analytical solution of the transport equation for electrons at a non-relativistic shock in the presence of synchrotron energy losses. We calculate the spectrum of accelerated (test) particles at any point upstream and downstream of the shock for an arbitrary diffusion coefficient, and we specialize the results to three cases: (1) diffusion constant in momentum [. D(p) =D0], (2) Bohm diffusion [. D(p) ∝p] and (3) Kolmogorov diffusion [. D(p) ∝p1/3]. Of special importance is the determination of the shape of the cut-off in the electron spectrum which depends on the diffusion properties felt by particles in the shock region. The formalism can be generalized to the case of a shock with an upstream precursor induced by the dynamical reaction of accelerated particles. © 2010 The Author. Journal compilation © 2010 RAS.

Valiviita J.,University of Portsmouth | Maartens R.,University of Portsmouth | Majerotto E.,University of Portsmouth | Majerotto E.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Yea