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Kanuchova Z.,National institute for astrophysics | Kanuchova Z.,Slovak Academy of Sciences | Brunetto R.,University Paris - Sud | Melita M.,Institute Astronomia y Fisica del Espacio IAFE | Strazzulla G.,National institute for astrophysics
Icarus | Year: 2012

The surfaces of small bodies in the outer Solar System are rich in organic compounds and carbonaceous refractories mixed with ices and silicates. As made clear by dedicated laboratory experiments space weathering (e.g. energetic ion bombardment) can produce red colored materials starting from bright and spectrally flat ices. In a classical scenario, the space weathering processes "nurture" alter the small bodies surface spectra but are in competition with resurfacing agents that restore the original colors, and the result of these competing processes continuously modifying the surfaces is supposed to be responsible for the observed spectral variety of those small bodies. However an alternative point of view is that the different colors are due to "nature" i.e. to the different primordial composition of different objects. In this paper we present a model, based on laboratory results, that gives an original contribution to the "nature" vs. "nurture" debate by addressing the case of surfaces showing different fractions of rejuvenated vs. space weathered surface, and calculating the corresponding color variations. We will show how a combination of increasing dose coupled to different resurfacing can reproduce the whole range of observations of small outer Solar System bodies. Here we demonstrate, for the first time that objects having a fully weathered material turn back in the color-color diagrams. At the same time, object with the different ratio of pristine and weathered surface areas lay on specific lines in color-color diagrams, if exposed to the same amount of irradiation. © 2012 Elsevier Inc.

Reynoso E.M.,Institute Astronomia y Fisica Del Espacio IAFE | Reynoso E.M.,University of Buenos Aires | Hughes J.P.,Rutgers University | Moffett D.A.,Furman University
Astronomical Journal | Year: 2013

Radio polarization observations provide essential information on the degree of order and orientation of magnetic fields, which themselves play a key role in the particle acceleration processes that take place in supernova remnants (SNRs). Here we present a radio polarization study of SN 1006, based on combined Very Large Array and Australia Telescope Compact Array observations at 20 cm that resulted in sensitive images with an angular resolution of 10 arcsec. The fractional polarization in the two bright radio and X-ray lobes of the SNR is measured to be 0.17, while in the southeastern sector, where the radio and non-thermal X-ray emission are much weaker, the polarization fraction reaches a value of 0.6 ± 0.2, close to the theoretical limit of 0.7. We interpret this result as evidence of a disordered, turbulent magnetic field in the lobes, where particle acceleration is believed to be efficient, and a highly ordered field in the southeast, where the acceleration efficiency has been shown to be very low. Utilizing the frequency coverage of our observations, an average rotation measure of ∼12 rad m-2 is determined from the combined data set, which is then used to obtain the intrinsic direction of the magnetic field vectors. While the orientation of magnetic field vectors across the SNR shell appear to be radial, a large fraction of the magnetic vectors lie parallel to the Galactic plane. Along the highly polarized southeastern rim, the field is aligned tangent to the shock, and therefore also nearly parallel to the Galactic plane. These results strongly suggest that the ambient field surrounding SN 1006 is aligned with this direction (i.e., from northeast to southwest) and that the bright lobes are due to a polar cap geometry. Our study establishes that the most efficient particle acceleration and generation of magnetic turbulence in SN 1006 is attained for shocks in which the magnetic field direction and shock normal are quasi-parallel, while inefficient acceleration and little to no generation of magnetic turbulence are obtained for the quasi-perpendicular case. © 2013. The American Astronomical Society. All rights reserved.

Suad L.A.,Instituto Argentino Of Radioastronomia Iar | Caiafa C.F.,Instituto Argentino Of Radioastronomia Iar | Caiafa C.F.,University of Buenos Aires | Arnal E.M.,Instituto Argentino Of Radioastronomia Iar | And 2 more authors.
Astronomy and Astrophysics | Year: 2014

Aims. The main goal of this work is to a have a new neutral hydrogen (H i) supershell candidate catalog to analyze their spatial distribution in the Galaxy and to carry out a statistical study of their main properties. Methods. This catalog was carried out making use of the Leiden-Argentine-Bonn (LAB) survey. The supershell candidates were identified using a combination of two techniques: a visual inspection plus an automatic searching algorithm. Our automatic algorithm is able to detect both closed and open structures. Results. A total of 566 supershell candidates were identified. Most of them (347) are located in the second Galactic quadrant, while 219 were found in the third one. About 98% of a subset of 190 structures (used to derive the statistical properties of the supershell candidates) are elliptical with a mean weighted eccentricity of 0.8 ± 0.1, and ~70% have their major axes parallel to the Galactic plane. The weighted mean value of the effective radius of the structures is ~160 pc. Owing to the ability of our automatic algorithm to detect open structures, we have also identified some "galactic chimney" candidates. We find an asymmetry between the second and third Galactic quadrants in the sense that in the second one we detect structures as far as 32 kpc, while for the 3rd one the farthest structure is detected at 17 kpc. The supershell surface density in the solar neighborhood is ~8 kpc-2, and decreases as we move farther away form the Galactic center. We have also compared our catalog with those by other authors. © ESO, 2014.

Luna G.J.M.,Institute Astronomia y Fisica Del Espacio IAFE | Sokoloski J.L.,Columbia University | Mukai K.,NASA | Mukai K.,University of Maryland Baltimore County | Nelson T.,University of Minnesota
Astronomy and Astrophysics | Year: 2013

Until recently, symbiotic binary systems in which a white dwarf accretes from a red giant were thought to be mainly a soft X-ray population. Here we describe the detection with the X-ray Telescope (XRT) on the Swift satellite of nine white dwarf symbiotics that were not previously known to be X-ray sources and one that had previously been detected as a supersoft X-ray source. The nine new X-ray detections were the result of a survey of 41 symbiotic stars, and they increase the number of symbiotic stars known to be X-ray sources by approximately 30%. The Swift/XRT telescope detected all of the new X-ray sources at energies greater than 2 keV. Their X-ray spectra are consistent with thermal emission and fall naturally into three distinct groups. The first group contains those sources with a single, highly absorbed hard component that we identify as probably coming from an accretion-disk boundary layer. The second group is composed of those sources with a single, soft X-ray spectral component that probably originates in a region where low-velocity shocks produce X-ray emission, i.e., a colliding-wind region. The third group consists of those sources with both hard and soft X-ray spectral components. We also find that unlike in the optical, where rapid, stochastic brightness variations from the accretion disk typically are not seen, detectable UV flickering is a common property of symbiotic stars. Supporting our physical interpretation of the two X-ray spectral components, simultaneous Swift UV photometry shows that symbiotic stars with harder X-ray emission tend to have stronger UV flickering, which is usually associated with accretion through a disk. To place these new observations in the context of previous work on X-ray emission from symbiotic stars, we modified and extended the α/β/γ classification scheme for symbiotic-star X-ray spectra that was introduced by Muerset et al. based upon observations with the ROSAT satellite, to include a new δ classification for sources with hard X-ray emission from the innermost accretion region. Because we have identified the elusive accretion component in the emission from a sample of symbiotic stars, our results have implications for the understanding of wind-fed mass transfer in wide binaries, and the accretion rate in one class of candidate progenitors of type Ia supernovae. © 2013 ESO.

Grumiller D.,Vienna University of Technology | Leston M.,Institute Astronomia y Fisica Del Espacio IAFE | Vassilevich D.,Federal University of ABC
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We provide a holographic description of two-dimensional dilaton gravity with anti-de Sitter boundary conditions. We find that the asymptotic symmetry algebra consists of a single copy of the Virasoro algebra with nonvanishing central charge and point out difficulties with the standard canonical treatment. We generalize our results to higher spin theories and thus provide the first examples of two-dimensional higher spin gravity with holographic description. For spin-3 gravity we find that the asymptotic symmetry algebra is a single copy of the W3 algebra. © 2014 American Physical Society.

Toledo-Roy J.C.,National Autonomous University of Mexico | Esquivel A.,National Autonomous University of Mexico | Velazquez P.F.,National Autonomous University of Mexico | Reynoso E.M.,Institute Astronomia y Fisica del Espacio IAFE | Reynoso E.M.,University of Buenos Aires
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present new 3D numerical simulations for Kepler's supernova remnant. In this work we revisit the possibility that the asymmetric shape of the remnant in X-rays is the product of a Type Ia supernova explosion which occurs inside the wind bubble previously created by an AGB companion star. Due to the large peculiar velocity of the system, the interaction of the strong AGB wind with the interstellar medium results in a bow shock structure. In this new model we propose that the AGB wind is anisotropic, with properties such as mass-loss rate and density having a latitude dependence, and that the orientation of the polar axis of the AGB star is not aligned with the direction of motion. The ejecta from the Type Ia supernova explosion is modelled using a power-law density profile, and we let the remnant evolve for 400 yr. We computed synthetic X-ray maps from the numerical results. We find that the estimated size and peculiar X-ray morphology of Kepler's supernova remnant are well reproduced by considering an AGB mass-loss rate of 10-5 M⊙ yr-1, a wind terminal velocity of 10 km s-1, an ambient medium density of 10-3 cm-3 and an explosion energy of 7 × 1050 erg. The obtained total X-ray luminosity of the remnant in this model reaches 6 × 1050 erg, which is within a factor of 2 of the observed value, and the time evolution of the luminosity shows a rate of decrease in recent decades of ∼2.4 per cent yr-1 that is consistent with the observations. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Paron S.,Institute Astronomia y Fisica Del Espacio IAFE | Paron S.,University of Buenos Aires | Petriella A.,Institute Astronomia y Fisica Del Espacio IAFE | Ortega M.E.,Institute Astronomia y Fisica Del Espacio IAFE
Astronomy and Astrophysics | Year: 2010

Aims. As part of a systematic study that we are performing to increase the observational evidence of triggered star formation in the surroundings of HII regions, we analyze the ISM around the HII region G35.673-00.847, a poorly studied source. Methods. Using data from the large-scale surveys Two Micron All Sky Survey, Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), MIPSGAL, Galactic Ring Survey (GRS), VLA Galactic Plane Survey (VGPS), and NRAO VLA Sky Survey (NVSS), we performed a multiwavelength study of G35.673-00.847 and its surroundings. Results. The mid-IR emission shows that G35.673-00.847 has an almost semi-ring like shape with a cut towards the galactic west. The radius of this semi-ring is about 1.′5 (∼1.6 pc, at the distance of ∼3.7 kpc). The distance was estimated from an HI absorption study and the analysis of the molecular gas. We find a molecular shell composed of several clumps distributed around the HII region, suggesting that its expansion is collecting the surrounding material. We identify several YSO candidates across the molecular shell. Finally, comparing the HII region dynamical age and the fragmentation time of the molecular shell, we discard the so-called collect and collapse as being the mechanism responsible for the YSO formation, suggesting that other processes such as radiative-driven implosion and/or small-scale Jeans gravitational instabilities operate. © 2010 ESO.

Reynoso E.M.,Institute Astronomia y Fisica del Espacio IAFE | Walsh A.J.,Curtin University Australia
Monthly Notices of the Royal Astronomical Society | Year: 2015

This paper presents a new study of the spectral index distribution of the supernova remnant (SNR) Puppis A. The nature of field compact sources is also investigated according to the measured spectral indices. This work is based on new observations of Puppis A and its surroundings performed with the Australia Telescope Compact Array in two configurations using the Compact Array Broad-band Backend centred at 1.75 GHz. We find that the global spectral index of Puppis A is α = -0.563 ± 0.013. Local variations have been detected, however this global index represents well the bulk of the SNR. At the SE, we found a pattern of parallel strips with a flat spectrum compatible with small-scale filaments, although not correlated in detail. The easternmost filament agrees with the idea that the SNR shock front is interacting with an external cloud. There is no evidence of the previously suggested correlation between emissivity and spectral index. A number of compact features are proposed to be evolved clumps of ejecta based on their spectral indices, although dynamic measurements are needed to confirm this hypothesis. We estimate precise spectral indices for the five previously known field sources, two of which are found to be double (one of them, probably triple), and catalogue 40 new sources. In the light of these new determinations, the extragalactic nature previously accepted for some compact sources is now in doubt. © 2015 The Authors.

Bengochea G.R.,Institute Astronomia y Fisica del Espacio IAFE
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

We show that when a procedure is made to remove the tension between a supernova Ia (SN Ia) data set and observations from BAO and CMB, there might be the case where the same SN Ia set built with two different light-curve fitters behaves as two separate and distinct supernova sets, and the tension found by some authors between supernova sets actually could be due to tension or inconsistency between fitters. We also show that the information of the fitter used in an SN Ia data set could be relevant to determine whether phantom type models are favored or not when such a set is combined with the BAO/CMB joint parameter. © 2010 Elsevier B.V.

Bengochea G.R.,Institute Astronomia y Fisica del Espacio IAFE
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

In the present work we analyze and compare the information coming from different observational data sets in the context of a sort of f(T) theories. We perform a joint analysis with measurements of the most recent type Ia supernovae (SNe Ia), Baryon Acoustic Oscillation (BAO), Cosmic Microwave Background radiation (CMB), Gamma-Ray Bursts data (GRBs) and Hubble parameter observations (OHD) to constraint the only new parameter these theories have. It is shown that when the new combined BAO/CMB parameter is used to put constraints, the result is different from previous works. We also show that when we include Observational Hubble Data (OHD) the simpler ΛCDM model is excluded to one sigma level, leading the effective equation of state of these theories to be of phantom type. Also, analyzing a tension criterion for SNe Ia and other observational sets, we obtain more consistent and better suited data sets to work with these theories. © 2010 Elsevier B.V.

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