Alejandro Córsico - Academia.edu (original) (raw)
Papers by Alejandro Córsico
Cornell University - arXiv, Dec 20, 2011
DAV stars, also called ZZ Ceti variables, are pulsating white dwarfs with atmospheres rich in H. ... more DAV stars, also called ZZ Ceti variables, are pulsating white dwarfs with atmospheres rich in H. Asteroseismology of DAV stars can provide valuable clues about the origin, structure and evolution of DA white dwarfs. Recently, a new DAV star, WD J191643.83+393849.7, has been discovered in the field of the Kepler spacecraft. It is expected that further monitoring of this star in the next years will enable astronomers to obtain the best lightcurve of a pulsating DA white dwarf ever recorded, and thus to know with unprecedented precision the hidden details of the internal structure of this star. In this paper, we perform a first asteroseismological analysis of WD J191643.83+393849.7 on the basis of fully evolutionary DA white-dwarf models. Specifically, we employ a complete set of evolutionary DA white-dwarf structures covering a wide range of effective temperatures, stellar masses, and H envelope thicknesses. These models have been obtained on the basis of a complete treatment of the evolutionary history of progenitors stars. We compute g-mode adiabatic pulsation periods for this set of models and compare them with the pulsation periods exhibited by WD J191643.83+393849.7. Based on a tentative estimation of the mean period spacing of the star, we find that the stellar mass should be substantially large (∼ > 0.80M ⊙), in agreement with the spectroscopically derived stellar mass. Also, from period-to-period fits we find an asteroseismological model characterised by a low effective temperature, rather high stellar mass and a thin H envelope. The possibility that this rather massive pulsating white dwarf can be further monitored with Kepler with a high degree of detail turns the star WD J191643.83+393849.7 into a promising and unique object to study the physics of crystallization and carbon/oxygen phase diagrams at high densities.
J. Isern, L. Althaus, S. Catalan, A. Corsico, E. Garcia–Berro, M. Salaris, S. Torres Institut de ... more J. Isern, L. Althaus, S. Catalan, A. Corsico, E. Garcia–Berro, M. Salaris, S. Torres Institut de Ciencies de l’Espai ICE(CSIC/IEEC), Campus UAB, 08193 Bellaterra, Spain Institut d’Estudis Espacials de Catalunya (IEEC), Ed. Nexus, c/Gran Capita, 08034 Barcelona, Spain Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Argentina CONICET, Argentina Center for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK Departament de Fisica Aplicada, Universitat Politecnica de Catalunya, c/Esteve Terrades 5, 08860 Castelldefels, Spain Astrophysics Research Institute, Liverpool John Moores University, 12 Quays House, Birkenhead, CH41 1LD, UK
Astronomy & Astrophysics, 2021
White dwarf stars are the most common end point of stellar evolution. The ultramassive white dwar... more White dwarf stars are the most common end point of stellar evolution. The ultramassive white dwarfs are of special interest as they are related to type Ia supernovae explosions, merger events, and fast radio bursts. Ultramassive white dwarfs are expected to harbour oxygen-neon (ONe) cores as a result of single standard stellar evolution. However, a fraction of them could have carbon-oxygen (CO) cores. Recent studies, based on the new observations provided by the Gaia space mission, indicate that a small fraction of the ultramassive white dwarfs experience a strong delay in their cooling, which cannot be solely attributed to the occurrence of crystallisation, thus requiring an unknown energy source able to prolong their life for long periods of time. In this study, we find that the energy released by 22Ne sedimentation in the deep interior of ultramassive white dwarfs with CO cores and high 22Ne content is consistent with the long cooling delay of these stellar remnants. On the basis...
We present an adiabatic pulsational study of subdwarf B stars based on full evolutionary models. ... more We present an adiabatic pulsational study of subdwarf B stars based on full evolutionary models. We computed six evolutionary sequences from the Main Sequence to the end of the Horizontal Branch. By applying different mass loss rates during the ascent through the Red Giant Branch, we obtained sdB star models in the Extreme Horizontal Branch with different surface parameters. We carry out a pulsational analysis of our sdB models. We assess the effects of the shape of the internal chemical profile on the radial and nonradial adiabatic pulsation spectrum. FULL TEXT IN SPANISH
Recently, low-mass white dwarf stars (< 0.5 M ) have been detected in open and globular cluste... more Recently, low-mass white dwarf stars (< 0.5 M ) have been detected in open and globular clusters. Though photometric variability has not been discovered in these objects yet, they are considered as potential pulsators. A powerful tool to study the internal structure and evolutionary properties of low-mass white dwarfs is Asteroseismology. Motivated by the possible detection of luminosity variations in the coming years, we present the first adiabatic and non adiabatic pulsational study applied to low-mass white dwarf stars in order to providing a theoretical basis to interpret the future observations.
We investigate the internal rotation profile of the GW Vir (PG1159-type) star PG 0122+200 by empl... more We investigate the internal rotation profile of the GW Vir (PG1159-type) star PG 0122+200 by employing an asteroseismological model that closely reproduces the observed periods of this star. We adopt a forward approach and two inversion methods based on the rotational splitting of the pulsation frequencies to explore the properties of the rotation of PG 0122+200. We found evidence for differential rotation in this star.
We present a large bank of chemical profiles and pulsation periods suited for asteroseismological... more We present a large bank of chemical profiles and pulsation periods suited for asteroseismological studies of ZZ Ceti (or DAV) variable stars. Our background equilibrium DA white dwarf models are the result of fully evolutionary computations that take into account the complete history of the progenitor stars from the ZAMS. The models are characterized by self-consistent chemical structures from the centre to the surface, and cover a wide range of stellar masses, effective temperatures, and H envelope thicknesses. We present dipole and quadrupole pulsation ggg-mode periods comfortably covering the interval of periods observed in ZZ Ceti stars. Complete tabulations of chemical profiles and pulsation periods to be used in asteroseismological period fits, as well as other quantities of interest, can be freely downloaded from our website (\url{http://www.fcaglp.unlp.edu.ar/evolgroup}
In file elm.dat are data presented in the middle and lower panels of Fig. 5 and 6. (1 data file).
White Dwarfs, 2003
Since some time ago, there has been a growing interest on the problem of stellar seismology since... more Since some time ago, there has been a growing interest on the problem of stellar seismology since the realization that this kind of study provides information on the internal structure of stars. As it is well known, white dwarfs (WDs) undergo non radial pulsations.
ABSTRACT We present the first outcomes of a theoretical study on the seismic properties of low-ma... more ABSTRACT We present the first outcomes of a theoretical study on the seismic properties of low-mass He-core white dwarfs on the basis of fully evolutionary models representative of these objects. This study is aimed to provide a theoretical basis from which to interpret present and future observations of variable low-mass white dwarfs.
Astrophysics and Space Science Proceedings, 2011
ABSTRACT Here, we report on the white dwarf catalog built from the SDSS DR7 (Cat. II/294). We hav... more ABSTRACT Here, we report on the white dwarf catalog built from the SDSS DR7 (Cat. II/294). We have applied automated techniques supplemented by complete, consistent human identifications of each candidate white dwarf spectrum. We make use of the latest SDSS reductions and white dwarf model atmosphere improvements in our spectral fits, providing logg and Teff determinations for each identified clean DA and DB where we use the word "clean" to identify spectra that show only features of non-magnetic, nonmixed, DA or DB stars. Our catalog includes all white dwarf stars from the earlier Kleinman et al. (2004, Cat. J/ApJ/607/426) and Eisenstein et al. (2006, Cat. J/ApJS/167/40) catalogs, although occasionally with different identifications. (1 data file).
We perform an asteroseismological study on the DAV star G117-B15A on the basis of a modern set of... more We perform an asteroseismological study on the DAV star G117-B15A on the basis of a modern set of fully evolutionary DA white dwarf models that have consistent chemical profiles at the core and the envelope. We found an asteroseismological model for G117-B15A that closely reproduces its observed pulsation periods. Then, we use the most recently measured value of the rate
A 20 % of white dwarf stars has hydrogen deficient atmospheres, known like no-DA white dwarfs. Th... more A 20 % of white dwarf stars has hydrogen deficient atmospheres, known like no-DA white dwarfs. The results of this work allow for the first time to study a possible evolutionary connection between different low mass and hydrogen deficient post-AGB stars, like DO white dwarfs, PG 1159, O(He), DB and RCrB, among others. FULL TEXT IN SPANISH
Astronomy & Astrophysics, 2015
Context. White dwarfs are nowadays routinely used as reliable cosmochronometers, allowing several... more Context. White dwarfs are nowadays routinely used as reliable cosmochronometers, allowing several stellar populations to be dated. Aims. We present new white dwarf evolutionary sequences for low-metallicity progenitors. This is motivated by the recent finding that residual H burning in low-mass white dwarfs resulting from Z = 0.0001 progenitors is the main energy source over a significant part of their evolution. Methods. White dwarf sequences have been derived from full evolutionary calculations that take the entire history of progenitor stars into account, including the thermally pulsing and the post-asymptotic giant branch (AGB) phases. Results. We show that for progenitor metallicities in the range 0.00003 Z 0.001, and in the absence of carbon enrichment from the occurrence of a third dredge-up episode, the resulting H envelope of the low-mass white dwarfs is thick enough to make stable H burning the most important energy source even at low luminosities. This has a significant impact on white dwarf cooling times. This result is independent of the adopted mass-loss rate during the thermally-pulsing and post-AGB phases and in the planetary nebulae stage. Conclusions. We conclude that in the absence of third dredge-up episodes, a significant part of the evolution of low-mass white dwarfs resulting from low-metallicity progenitors is dominated by stable H burning. Our study opens the possibility of using the observed white dwarf luminosity function of low-metallicity globular clusters to constrain the efficiency of third dredge up episodes during the thermally-pulsing AGB phase of low-metallicity progenitors.
Cornell University - arXiv, Dec 20, 2011
DAV stars, also called ZZ Ceti variables, are pulsating white dwarfs with atmospheres rich in H. ... more DAV stars, also called ZZ Ceti variables, are pulsating white dwarfs with atmospheres rich in H. Asteroseismology of DAV stars can provide valuable clues about the origin, structure and evolution of DA white dwarfs. Recently, a new DAV star, WD J191643.83+393849.7, has been discovered in the field of the Kepler spacecraft. It is expected that further monitoring of this star in the next years will enable astronomers to obtain the best lightcurve of a pulsating DA white dwarf ever recorded, and thus to know with unprecedented precision the hidden details of the internal structure of this star. In this paper, we perform a first asteroseismological analysis of WD J191643.83+393849.7 on the basis of fully evolutionary DA white-dwarf models. Specifically, we employ a complete set of evolutionary DA white-dwarf structures covering a wide range of effective temperatures, stellar masses, and H envelope thicknesses. These models have been obtained on the basis of a complete treatment of the evolutionary history of progenitors stars. We compute g-mode adiabatic pulsation periods for this set of models and compare them with the pulsation periods exhibited by WD J191643.83+393849.7. Based on a tentative estimation of the mean period spacing of the star, we find that the stellar mass should be substantially large (∼ > 0.80M ⊙), in agreement with the spectroscopically derived stellar mass. Also, from period-to-period fits we find an asteroseismological model characterised by a low effective temperature, rather high stellar mass and a thin H envelope. The possibility that this rather massive pulsating white dwarf can be further monitored with Kepler with a high degree of detail turns the star WD J191643.83+393849.7 into a promising and unique object to study the physics of crystallization and carbon/oxygen phase diagrams at high densities.
J. Isern, L. Althaus, S. Catalan, A. Corsico, E. Garcia–Berro, M. Salaris, S. Torres Institut de ... more J. Isern, L. Althaus, S. Catalan, A. Corsico, E. Garcia–Berro, M. Salaris, S. Torres Institut de Ciencies de l’Espai ICE(CSIC/IEEC), Campus UAB, 08193 Bellaterra, Spain Institut d’Estudis Espacials de Catalunya (IEEC), Ed. Nexus, c/Gran Capita, 08034 Barcelona, Spain Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Argentina CONICET, Argentina Center for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK Departament de Fisica Aplicada, Universitat Politecnica de Catalunya, c/Esteve Terrades 5, 08860 Castelldefels, Spain Astrophysics Research Institute, Liverpool John Moores University, 12 Quays House, Birkenhead, CH41 1LD, UK
Astronomy & Astrophysics, 2021
White dwarf stars are the most common end point of stellar evolution. The ultramassive white dwar... more White dwarf stars are the most common end point of stellar evolution. The ultramassive white dwarfs are of special interest as they are related to type Ia supernovae explosions, merger events, and fast radio bursts. Ultramassive white dwarfs are expected to harbour oxygen-neon (ONe) cores as a result of single standard stellar evolution. However, a fraction of them could have carbon-oxygen (CO) cores. Recent studies, based on the new observations provided by the Gaia space mission, indicate that a small fraction of the ultramassive white dwarfs experience a strong delay in their cooling, which cannot be solely attributed to the occurrence of crystallisation, thus requiring an unknown energy source able to prolong their life for long periods of time. In this study, we find that the energy released by 22Ne sedimentation in the deep interior of ultramassive white dwarfs with CO cores and high 22Ne content is consistent with the long cooling delay of these stellar remnants. On the basis...
We present an adiabatic pulsational study of subdwarf B stars based on full evolutionary models. ... more We present an adiabatic pulsational study of subdwarf B stars based on full evolutionary models. We computed six evolutionary sequences from the Main Sequence to the end of the Horizontal Branch. By applying different mass loss rates during the ascent through the Red Giant Branch, we obtained sdB star models in the Extreme Horizontal Branch with different surface parameters. We carry out a pulsational analysis of our sdB models. We assess the effects of the shape of the internal chemical profile on the radial and nonradial adiabatic pulsation spectrum. FULL TEXT IN SPANISH
Recently, low-mass white dwarf stars (< 0.5 M ) have been detected in open and globular cluste... more Recently, low-mass white dwarf stars (< 0.5 M ) have been detected in open and globular clusters. Though photometric variability has not been discovered in these objects yet, they are considered as potential pulsators. A powerful tool to study the internal structure and evolutionary properties of low-mass white dwarfs is Asteroseismology. Motivated by the possible detection of luminosity variations in the coming years, we present the first adiabatic and non adiabatic pulsational study applied to low-mass white dwarf stars in order to providing a theoretical basis to interpret the future observations.
We investigate the internal rotation profile of the GW Vir (PG1159-type) star PG 0122+200 by empl... more We investigate the internal rotation profile of the GW Vir (PG1159-type) star PG 0122+200 by employing an asteroseismological model that closely reproduces the observed periods of this star. We adopt a forward approach and two inversion methods based on the rotational splitting of the pulsation frequencies to explore the properties of the rotation of PG 0122+200. We found evidence for differential rotation in this star.
We present a large bank of chemical profiles and pulsation periods suited for asteroseismological... more We present a large bank of chemical profiles and pulsation periods suited for asteroseismological studies of ZZ Ceti (or DAV) variable stars. Our background equilibrium DA white dwarf models are the result of fully evolutionary computations that take into account the complete history of the progenitor stars from the ZAMS. The models are characterized by self-consistent chemical structures from the centre to the surface, and cover a wide range of stellar masses, effective temperatures, and H envelope thicknesses. We present dipole and quadrupole pulsation ggg-mode periods comfortably covering the interval of periods observed in ZZ Ceti stars. Complete tabulations of chemical profiles and pulsation periods to be used in asteroseismological period fits, as well as other quantities of interest, can be freely downloaded from our website (\url{http://www.fcaglp.unlp.edu.ar/evolgroup}
In file elm.dat are data presented in the middle and lower panels of Fig. 5 and 6. (1 data file).
White Dwarfs, 2003
Since some time ago, there has been a growing interest on the problem of stellar seismology since... more Since some time ago, there has been a growing interest on the problem of stellar seismology since the realization that this kind of study provides information on the internal structure of stars. As it is well known, white dwarfs (WDs) undergo non radial pulsations.
ABSTRACT We present the first outcomes of a theoretical study on the seismic properties of low-ma... more ABSTRACT We present the first outcomes of a theoretical study on the seismic properties of low-mass He-core white dwarfs on the basis of fully evolutionary models representative of these objects. This study is aimed to provide a theoretical basis from which to interpret present and future observations of variable low-mass white dwarfs.
Astrophysics and Space Science Proceedings, 2011
ABSTRACT Here, we report on the white dwarf catalog built from the SDSS DR7 (Cat. II/294). We hav... more ABSTRACT Here, we report on the white dwarf catalog built from the SDSS DR7 (Cat. II/294). We have applied automated techniques supplemented by complete, consistent human identifications of each candidate white dwarf spectrum. We make use of the latest SDSS reductions and white dwarf model atmosphere improvements in our spectral fits, providing logg and Teff determinations for each identified clean DA and DB where we use the word "clean" to identify spectra that show only features of non-magnetic, nonmixed, DA or DB stars. Our catalog includes all white dwarf stars from the earlier Kleinman et al. (2004, Cat. J/ApJ/607/426) and Eisenstein et al. (2006, Cat. J/ApJS/167/40) catalogs, although occasionally with different identifications. (1 data file).
We perform an asteroseismological study on the DAV star G117-B15A on the basis of a modern set of... more We perform an asteroseismological study on the DAV star G117-B15A on the basis of a modern set of fully evolutionary DA white dwarf models that have consistent chemical profiles at the core and the envelope. We found an asteroseismological model for G117-B15A that closely reproduces its observed pulsation periods. Then, we use the most recently measured value of the rate
A 20 % of white dwarf stars has hydrogen deficient atmospheres, known like no-DA white dwarfs. Th... more A 20 % of white dwarf stars has hydrogen deficient atmospheres, known like no-DA white dwarfs. The results of this work allow for the first time to study a possible evolutionary connection between different low mass and hydrogen deficient post-AGB stars, like DO white dwarfs, PG 1159, O(He), DB and RCrB, among others. FULL TEXT IN SPANISH
Astronomy & Astrophysics, 2015
Context. White dwarfs are nowadays routinely used as reliable cosmochronometers, allowing several... more Context. White dwarfs are nowadays routinely used as reliable cosmochronometers, allowing several stellar populations to be dated. Aims. We present new white dwarf evolutionary sequences for low-metallicity progenitors. This is motivated by the recent finding that residual H burning in low-mass white dwarfs resulting from Z = 0.0001 progenitors is the main energy source over a significant part of their evolution. Methods. White dwarf sequences have been derived from full evolutionary calculations that take the entire history of progenitor stars into account, including the thermally pulsing and the post-asymptotic giant branch (AGB) phases. Results. We show that for progenitor metallicities in the range 0.00003 Z 0.001, and in the absence of carbon enrichment from the occurrence of a third dredge-up episode, the resulting H envelope of the low-mass white dwarfs is thick enough to make stable H burning the most important energy source even at low luminosities. This has a significant impact on white dwarf cooling times. This result is independent of the adopted mass-loss rate during the thermally-pulsing and post-AGB phases and in the planetary nebulae stage. Conclusions. We conclude that in the absence of third dredge-up episodes, a significant part of the evolution of low-mass white dwarfs resulting from low-metallicity progenitors is dominated by stable H burning. Our study opens the possibility of using the observed white dwarf luminosity function of low-metallicity globular clusters to constrain the efficiency of third dredge up episodes during the thermally-pulsing AGB phase of low-metallicity progenitors.