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Sanchez-Conde M.A.,Kavli Institute for Particle Astrophysics and Cosmology | Prada F.,Campus of International Excellence UAMCSIC | Prada F.,Autonomous University of Madrid | Prada F.,Institute Astrofisica Of Andalucia Iaa Csic
Monthly Notices of the Royal Astronomical Society | Year: 2014

In the standard cold dark matter (CDM) theory for understanding the formation of structure in theUniverse, there exists a tight connection between the properties of darkmatter (DM) haloes, and their formation epochs. Such relation can be expressed in terms of a single key parameter, namely the halo concentration. In this work, we examine the median concentration-mass relation, c(M), at present time, over more than 20 orders of magnitude in halo mass, i.e. from tiny Earth-mass microhaloes up to galaxy clusters. The c(M) model proposed by Prada et al. (2012), which links the halo concentration with the rms amplitude of matter linear fluctuations, describes remarkably well all the available N-body simulation data down to ~10-6 h -1M( microhaloes. A clear fattening of the halo concentration-mass relation towards smaller masses is observed, that excludes the commonly adopted power-law c(M) models, and stands as a natural prediction for the CDM paradigm. We provide a parametrization for the c(M) relation that works accurately for all halo masses. This feature in the c(M) relation at low masses has decisive consequences e.g. for γ -ray DM searches, as it implies more modest boosts of the DM annihilation flux due to substructure, i.e. ~35 for galaxy clusters and ~15 for galaxies like our own, as compared to those huge values adopted in the literature that rely on such power-law c(M) extrapolations. We provide a parametrization of the boosts that can be safely used for dwarfs to galaxy cluster-size haloes. © 2014 The Authors.

Barcelo C.,Institute Astrofisica Of Andalucia Iaa Csic | Carballo-Rubio R.,Institute Astrofisica Of Andalucia Iaa Csic | Garay L.J.,Complutense University of Madrid | Garay L.J.,CSIC - Institute for the Structure of Matter | Jannes G.,Charles III University of Madrid
Classical and Quantum Gravity | Year: 2015

It is logically possible that regularly evaporating black holes (REBHs) exist in nature. In fact, the prevalent theoretical view is that these are indeed the real objects behind the curtain in astrophysical scenarios. There are several proposals for regularizing the classical singularity of black holes so that their formation and evaporation do not lead to information-loss problems. One characteristic is shared by most of these proposals: these REBHs present long-lived trapping horizons, with absolutely enormous evaporation lifetimes in whatever measure. Guided by the discomfort with these enormous and thus inaccessible lifetimes, we elaborate here on an alternative regularization of the classical singularity, previously proposed by the authors in an emergent gravity framework, which leads to a completely different scenario. In our scheme the collapse of a stellar object would result in a genuine time-symmetric bounce, which in geometrical terms amounts to the connection of a black-hole geometry with a white-hole geometry in a regular manner. The two most differential characteristics of this proposal are: (i) the complete bouncing geometry is a solution of standard classical general relativity everywhere except in a transient region that necessarily extends beyond the gravitational radius associated with the total mass of the collapsing object; and (ii) the duration of the bounce as seen by external observers is very brief (fractions of milliseconds for neutron-star-like collapses). This scenario motivates the search for new forms of stellar equilibrium different from black holes. In a brief epilogue we compare our proposal with a similar geometrical setting recently proposed by Haggard and Rovelli. © 2015 IOP Publishing Ltd.

Barcelo C.,Institute Astrofisica Of Andalucia Iaa Csic | Carballo-Rubio R.,Institute Astrofisica Of Andalucia Iaa Csic | Garay L.J.,Complutense University of Madrid | Garay L.J.,CSIC - Institute for the Structure of Matter | Gomez-Escalante R.,Complutense University of Madrid
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We reappraise some of the hybrid classical-quantum models proposed in the literature with the goal of retrieving some of their common characteristics. In particular, first, we analyze in detail the Peres-Terno argument regarding the inconsistency of hybrid quantizations of the Sudarshan type. We show that to accept such hybrid formalism entails the necessity of dealing with additional degrees of freedom beyond those in the straight complete quantization of the system. Second, we recover a similar enlargement of degrees of freedom in the so-called statistical hybrid models. Finally, we use Wigner's quantization of a simple model to illustrate how in hybrid systems the subsystems are never purely classical or quantum. A certain degree of quantumness (classicality) is being exchanged between the different sectors of the theory, which in this particular unphysical toy model makes them undistinguishable. © 2012 American Physical Society.

Barcelo C.,Institute Astrofisica Of Andalucia Iaa Csic | Carballo-Rubio R.,Institute Astrofisica Of Andalucia Iaa Csic | Garay L.J.,Complutense University of Madrid | Garay L.J.,CSIC - Institute for the Structure of Matter
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

It is commonly accepted that general relativity is the only solution to the consistency problem that appears when trying to build a theory of interacting gravitons (massless spin-2 particles). Padmanabhan's 2008 thought-provoking analysis raised some concerns that are having resonance in the community. In this paper we present the self-coupling problem in detail and explicitly solve the infinite-iterations scheme associated with it for the simplest theory of a graviton field, which corresponds to an irreducible spin-2 representation of the Poincaré group. We make explicit the nonuniqueness problem by finding an entire family of solutions to the self-coupling problem. Then we show that the only resulting theory which implements a deformation of the original gauge symmetry happens to have essentially the structure of unimodular gravity. This makes plausible the possibility of a natural solution to the first cosmological constant problem in theories of emergent gravity. Later on, we change for the sake of completeness the starting free-field theory to Fierz-Pauli theory, an equivalent theory but with a larger gauge symmetry. We indicate how to carry out the infinite summation procedure in a similar way. Overall, we conclude that as long as one requires the (deformed) preservation of internal gauge invariance, one naturally recovers the structure of unimodular gravity or general relativity but in a version that explicitly shows the underlying Minkowski spacetime, in the spirit of Rosen's flat-background bimetric theory. © 2014 American Physical Society.

Ramos-Larios G.,Institute Astrofisica Of Andalucia Iaa Csic | Guerrero M.A.,Institute Astrofisica Of Andalucia Iaa Csic | Suarez O.,University of Nice Sophia Antipolis | Miranda L.F.,CSIC - Institute of Refrigeration | Gomez J.F.,Institute Astrofisica Of Andalucia Iaa Csic
Astronomy and Astrophysics | Year: 2012

The most massive AGB stars are expected to result in heavily obscured post-AGB stars, proto-PNe and PNe with highly axisymmetric morphologies. To investigate this evolutionary connection, we have selected a sample of 165 presumably obscured IRAS post-AGB star and PN candidates and obtained near-IR JHK images for 164 of them. These images, in conjunction with DSS, 2MASS, Spitzer GLIMPSE, MSX, AKARI, and IRAS archival data, have allowed us to identify the near-IR counterparts of 154 of these sources, providing reliable finding charts and coordinates. Near-IR narrow-band Brγ, H 2, and K continuum images were acquired for 6 of these sources that were found to be resolved in near-IR JHK images. Among the extended post-AGB source and PN candidates, three are round and seven have bipolar morphologies. Five of the extended sources are ionized and may have thus entered the PN stage. We note that all extended sources with water maser emission have bipolar morphology. We have investigated the Galactic distribution of sources with the largest flux drop from the 9 μm AKARI band to the near-IR J band and found that the width of the distribution in Galactic latitude is consistent with those of bipolar PNe and DUPLEX (DUst-Prominent Longitudinally EXtended) sources. © 2012 ESO.

Rodriguez-Lopez C.,Institute Astrofisica Of Andalucia Iaa Csic | Macdonald J.,University of Delaware | Moya A.,CSIC - National Institute of Aerospace Technology
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

We present the results of the first theoretical non-radial, non-adiabatic pulsational study of M dwarf stellar models with masses in the range 0.1-0.5M⊙. We find the fundamental radial mode to be unstable due to an ε mechanism, caused by deuterium (D) burning for the young 0.1 and 0.2M⊙ models, by non-equilibrium He3 burning for the 0.2 and 0.25M⊙ models of 104Myr and by a flux-blocking mechanism for the partially convective 0.4 and 0.5M⊙ models once they reach the age of 500Myr. The periods of the overstable modes excited by the D burning are in the range 4.2-5.2h for the 0.1M⊙ models and is of the order of 8.4h for the 0.2M⊙ models. The periods of the modes excited by He3 burning and flux blocking are in the range 23-40min. The more massive and oldest models are more promising for the observational detection of pulsations as their ratio of instability e-folding time to age is more favourable. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Guerrero M.A.,Institute Astrofisica Of Andalucia Iaa Csic | Guerrero M.A.,Macquarie University | De Marco O.,Macquarie University
Astronomy and Astrophysics | Year: 2013

The occurrence of stellar wind in the central star of a planetary nebula (CSPN) can be revealed by the presence of P Cygni profiles of high-excitation lines overimposed on its stellar continuum. We examined the entire Far-Ultraviolet Spectroscopic Explorer (FUSE) archive and merged all useful spectroscopic observations of CSPNe to produce the highest quality spectra that can be used to assess the frequency of stellar winds. Furthermore, the individual spectra of each CSPN were compared to search for variability in the P Cygni profile. P Cygni profiles of high-excitation lines have been found in 44 CSPNe, with a clear correlation between the ionization potential of the lines and the effective temperature of the star. We introduce a prescription to derive the terminal wind velocity (v∞) from saturated and unsaturated P Cygni profiles and provide new values of v∞ for these stars. Another 23 CSPNe do not show P Cygni profiles, or else their data in the FUSE archive are not conclusive enough to determine the occurrence of P Cygni profiles. Variability in the P Cygni profile of high-excitation, far-UV lines is found for the first time in six CSPNe, namely Hen 2-131, NGC 40, NGC 1535, NGC 2392, Sp 3, and SwSt 1. This increases up to 13 the number of CSPNe with variable P Cygni profiles in the UV, including those previously reported using IUE or FUSE observations. Variability is seen primarily in the unsaturated P v and Si iv lines, but also in saturated C iii and O vi lines. The CSPNe with variable P Cygni profiles have similar stellar properties (relatively low log (g) and Teff) that suggest they are less evolved CSPNe. Some of the CSPNe with variable P Cygni profiles show O vi lines, while their effective temperature is insufficient to produce this ion. We suggest that this ion is produced by Auger ionization from X-rays associated to shocks in their stellar winds, as is the case in massive OB stars of high ionization potential ions that cannot be abundantly produced by photoionizations. © ESO, 2013.

Delgado A.J.,Institute Astrofisica Of Andalucia Iaa Csic | Djupvik A.A.,Nordic Optical Telescope NOT | Costado M.T.,Institute Astrofisica Of Andalucia Iaa Csic | Alfaro E.J.,Institute Astrofisica Of Andalucia Iaa Csic
Monthly Notices of the Royal Astronomical Society | Year: 2013

We have performed multiband UBVRCICJHKS photometry of two young clusters located at large Galactocentric distances in the direction of the Perseus spiral arm. The obtained distances and colour excesses amount to 3.9 ± 0.11 kpc, E(B - V) = 0.62 ± 0.05 for Berkeley 94, and 4.3 ± 0.15 kpc, E(B - V) = 0.58 ± 0.06 for Berkeley 96. The respective ages, as measured from the comparison of the upper colour-magnitude diagrams to model isochrones, amount to log10Age(yr) = 7.5 ± 0.07 and 7.0 ± 0.07, respectively. A sequence of optical pre-main-sequence (PMS) members is proposed in both clusters. In addition, samples of objects showing (H - KS) excess are found. Part of these are suggested to be PMS cluster members of lower mass than the optical candidates. The spatial distribution of these sources, the comparison to Galactic models and to the expected number of contaminating distant red galaxies, and the spectral energy distribution in particular cases support this suggestion. The spatial distributions shown by members in different mass ranges can be interpreted in terms of the results from numerical simulations. According to these, different initial conditions and evolutionary dynamical paths are suggested for the clusters. Berkeley 94 would have formed under supervirial conditions, and followed the so-called warm collapse model in its evolution, whereas Berkeley 96 would have formed with a subvirial structure, and would have evolved following a cold collapse path. Both processeswould be able to reproduce the suggested degree of mass segregation and their spatial distribution by mass range. Finally, the mass distributions of the clusters, from the most massive stars down to PMS stars around 1.3M⊙, are calculated. An acceptable general agreement with the Salpeter initial mass function slope is found. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Carballo-Rubio R.,Institute Astrofisica Of Andalucia Iaa Csic
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

To guarantee the stability of the cosmological constant sector against radiative corrections coming from quantum matter fields, one of the most natural ingredients to invoke is the symmetry under scale transformations of the gravitational field. Previous attempts to follow this path have nevertheless failed in providing a consistent picture. Here, we point out that this failure is intimately tied up to an assumption that is typically embedded in modern studies of the gravitational interaction: invariance under the full group of diffeomorphisms. We base the discussion on the gravitational theory known as Weyl transverse gravity. While leading to the same classical solutions as general relativity, and so to the same classical phenomenology, we show that in the presence of quantum matter (i) the degeneracy between these theories is broken (general relativity exhibits the well-known cosmological constant problem, while in Weyl transverse gravity, the cosmological constant sector is protected due to gravitational scale invariance), and (ii) this is possible as the result of abandoning the assumption of full diffeomorphism invariance, which permits circumventing classic results on scale-invariance anomalies and guarantees that gravitational scale invariance survives quantum corrections. Both results signal new directions in the quest of finding an ultraviolet completion of gravity. © 2015 American Physical Society.

Castro-Tirado A.J.,Institute Astrofisica Of Andalucia Iaa Csic
Advances in Astronomy | Year: 2010

This paper presents a historical introduction to the field of Robotic Astronomy, from the point of view of a scientist working in this field for more than a decade. The author discusses the basic definitions, the differing telescope control operating systems, observatory managers, as well as a few current scientific applications. Copyright © 2010 Alberto Javier Castro-Tirado.

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