The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Souza Oliveira Kepler - One of the best experts on this subject based on the ideXlab platform.
-
White Dwarf Stars
International Journal of Modern Physics: Conference Series, 2017Co-Authors: Souza Oliveira Kepler, Alejandra D. Romero, Ingrid Pelisoli, Gustavo OuriqueAbstract:White Dwarf Stars are the final stage of most Stars, born single or in multiple systems. We discuss the identification, magnetic fields, and mass distribution for white Dwarfs detected from spectra obtained by the Sloan Digital Sky Survey up to Data Release 13 in 2016, which lead to the increase in the number of spectroscopically identified white Dwarf Stars from 5000 to 39000. This number includes only white Dwarf Stars with log g >= 6.5 Stars, i.e., excluding the Extremely Low Mass white Dwarfs, which are necessarily the byproduct of stellar interaction.
-
New white Dwarf Stars in the Sloan Digital Sky Survey Data Release 10
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: Souza Oliveira Kepler, Alejandra D. Romero, Ingrid Pelisoli, Gustavo Ourique, Detlev Koester, S. J. Kleinman, Atsuko Nitta, Daniel J. Eisenstein, J. E. S. Costa, B. KülebiAbstract:We report the discovery of 9 089 new spectroscopically confirmed white Dwarfs and subDwarfs in the Sloan Digital Sky Survey Data Release 10. We obtain Teff, log g and mass for hydrogen atmosphere white Dwarf Stars (DAs) and helium atmosphere white Dwarf Stars (DBs), and estimate the calcium/helium abundances for the white Dwarf Stars with metallic lines (DZs) and carbon/helium for carbon dominated spectra DQs. We found 1 central star of a planetary nebula, 2 new oxygen spectra on helium atmosphere white Dwarfs, 71 DQs, 42 hot DO/PG1159s, 171 white Dwarf+main sequence star binaries, 206 magnetic DAHs, 327 continuum dominated DCs, 397 metal polluted white Dwarfs, 450 helium dominated white Dwarfs, 647 subDwarfs and 6888 new hydrogen dominated white Dwarf Stars.
-
Discovery of five new massive pulsating white Dwarf Stars
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: B. G. Castanheira, Souza Oliveira Kepler, Atsuko Nitta, Scot Kleinman, Luciano FragaAbstract:Using the SOuthern Astrophysical Research telescope (SOAR) Optical Imager at the SOAR 4.1 m telescope, we report on the discovery of five new massive pulsating white Dwarf Stars. Our results represent an increase of about 20 per cent in the number of massive pulsators. We have detected both short and long periods, low and high amplitude pulsation modes, covering the whole range of the ZZ Ceti instability strip.In this paper, we present a first seismological study of the new massive pulsators based on the few frequencies detected. Our analysis indicates that these Stars have masses higher than average, in agreement with the spectroscopic determinations. In addition, we study for the first time the ensemble properties of the pulsating white Dwarf Stars with masses above 0.8 M ⊙ . We found a bimodal distribution of the main pulsation period with the effective temperature for the massive DAVs, which indicates mode selection mechanisms.
-
The most massive pulsating white Dwarf Stars
Proceedings of the International Astronomical Union, 2013Co-Authors: B. G. Castanheira, Souza Oliveira KeplerAbstract:AbstractMassive pulsating white Dwarf Stars are extremely rare, because of their small size and because they are the final product of high-mass Stars, which are less common. Because of their intrinsic smaller size, they are fainter than the normal size white Dwarf Stars. The motivation to look for this type of Stars is to be able to study in detail their internal structure and also derive generic properties for the sub-class of variables, the massive ZZ Ceti Stars. Our goal is to investigate whether the internal structures of these Stars differ from the lower-mass ones, which in turn could have been resultant from the previous evolutionary stages.In this paper, we present the ensemble seismological analysis of the known massive pulsating white Dwarf Stars. Some of these pulsating Stars might have substantial crystallized cores, which would allow us to probe solid physics in extreme conditions.
-
New Pulsating DB White Dwarf Stars From The Sloan Digital Sky Survey
The Astrophysical Journal, 2008Co-Authors: Atsuko Nitta, Souza Oliveira Kepler, Fergal Mullally, Jurek Krzesinski, Scot Kleinman, Anjum S. Mukadam, R. E. Nather, Travis S. Metcalfe, Denis J. Sullivan, Susan E. ThompsonAbstract:We are searching for new He atmosphere white Dwarf pulsators (DBVs) based on the newly found white Dwarf Stars from the spectra obtained by the Sloan Digital Sky Survey. DBVs pulsate at hotter temperature ranges than their better known cousins, the H atmosphere white Dwarf pulsators (DAVs or ZZ Ceti Stars). Since the evolution of white Dwarf Stars is characterized by cooling, asteroseismological studies of DBVs give us opportunities to study white Dwarf structure at a different evolutionary stage than the DAVs. The hottest DBVs are thought to have neutrino luminosities exceeding their photon luminosities, a quantity measurable through asteroseismology. Therefore, they can also be used to study neutrino physics in the stellar interior. So far we have discovered nine new DBVs, doubling the number of previously known DBVs. Here we report the new pulsators' light curves and power spectra.
Atsuko Nitta - One of the best experts on this subject based on the ideXlab platform.
-
New white Dwarf Stars in the Sloan Digital Sky Survey Data Release 10
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: Souza Oliveira Kepler, Alejandra D. Romero, Ingrid Pelisoli, Gustavo Ourique, Detlev Koester, S. J. Kleinman, Atsuko Nitta, Daniel J. Eisenstein, J. E. S. Costa, B. KülebiAbstract:We report the discovery of 9 089 new spectroscopically confirmed white Dwarfs and subDwarfs in the Sloan Digital Sky Survey Data Release 10. We obtain Teff, log g and mass for hydrogen atmosphere white Dwarf Stars (DAs) and helium atmosphere white Dwarf Stars (DBs), and estimate the calcium/helium abundances for the white Dwarf Stars with metallic lines (DZs) and carbon/helium for carbon dominated spectra DQs. We found 1 central star of a planetary nebula, 2 new oxygen spectra on helium atmosphere white Dwarfs, 71 DQs, 42 hot DO/PG1159s, 171 white Dwarf+main sequence star binaries, 206 magnetic DAHs, 327 continuum dominated DCs, 397 metal polluted white Dwarfs, 450 helium dominated white Dwarfs, 647 subDwarfs and 6888 new hydrogen dominated white Dwarf Stars.
-
Discovery of five new massive pulsating white Dwarf Stars
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: B. G. Castanheira, Souza Oliveira Kepler, Atsuko Nitta, Scot Kleinman, Luciano FragaAbstract:Using the SOuthern Astrophysical Research telescope (SOAR) Optical Imager at the SOAR 4.1 m telescope, we report on the discovery of five new massive pulsating white Dwarf Stars. Our results represent an increase of about 20 per cent in the number of massive pulsators. We have detected both short and long periods, low and high amplitude pulsation modes, covering the whole range of the ZZ Ceti instability strip.In this paper, we present a first seismological study of the new massive pulsators based on the few frequencies detected. Our analysis indicates that these Stars have masses higher than average, in agreement with the spectroscopic determinations. In addition, we study for the first time the ensemble properties of the pulsating white Dwarf Stars with masses above 0.8 M ⊙ . We found a bimodal distribution of the main pulsation period with the effective temperature for the massive DAVs, which indicates mode selection mechanisms.
-
New Pulsating DB White Dwarf Stars From The Sloan Digital Sky Survey
The Astrophysical Journal, 2008Co-Authors: Atsuko Nitta, Souza Oliveira Kepler, Fergal Mullally, Jurek Krzesinski, Scot Kleinman, Anjum S. Mukadam, R. E. Nather, Travis S. Metcalfe, Denis J. Sullivan, Susan E. ThompsonAbstract:We are searching for new He atmosphere white Dwarf pulsators (DBVs) based on the newly found white Dwarf Stars from the spectra obtained by the Sloan Digital Sky Survey. DBVs pulsate at hotter temperature ranges than their better known cousins, the H atmosphere white Dwarf pulsators (DAVs or ZZ Ceti Stars). Since the evolution of white Dwarf Stars is characterized by cooling, asteroseismological studies of DBVs give us opportunities to study white Dwarf structure at a different evolutionary stage than the DAVs. The hottest DBVs are thought to have neutrino luminosities exceeding their photon luminosities, a quantity measurable through asteroseismology. Therefore, they can also be used to study neutrino physics in the stellar interior. So far we have discovered nine new DBVs, doubling the number of previously known DBVs. Here we report the new pulsators' light curves and power spectra.
-
A Catalog of Spectroscopically Identified White Dwarf Stars in the First Data Release of the Sloan Digital Sky Survey
The Astrophysical Journal, 2004Co-Authors: Scot Kleinman, Atsuko Nitta, Daniel J. Eisenstein, James Liebert, Hugh C Harris, Jurek Krzesinski, Jeffrey A Munn, Conard C Dahn, Suzanne L Hawley, Jeffrey R PierAbstract:We present the full spectroscopic white Dwarf and hot subDwarf sample from the Sloan Digital Sky Survey (SDSS) first data release, DR1. We find 2551 white Dwarf Stars of various types, 240 hot subDwarf Stars, and an additional 144 objects we have identified as uncertain white Dwarf Stars. Of the white Dwarf Stars, 1888 are nonmagnetic DA types and 171 are nonmagnetic DBs. The remaining (492) objects consist of all different types of white Dwarf Stars: DO, DQ, DC, DH, DZ, hybrid Stars such as DAB, etc., and those with nondegenerate companions. We fit the DA and DB spectra with a grid of models to determine the Teff and log g for each object. For all objects, we provide coordinates, proper motions, SDSS photometric magnitudes, and enough information to retrieve the spectrum/image from the SDSS public database. This catalog nearly doubles the known sample of spectroscopically identified white Dwarf Stars. In the DR1 imaged area of the sky, we increase the known sample of white Dwarf Stars by a factor of 8.5. We also comment on several particularly interesting objects in this sample.
-
a catalog of spectroscopically identified white Dwarf Stars in the first data release of the sloan digital sky survey
arXiv: Astrophysics, 2004Co-Authors: S. J. Kleinman, Atsuko Nitta, Daniel J. Eisenstein, James Liebert, Hugh C Harris, Jurek Krzesinski, Jeffrey A Munn, Conard C Dahn, Suzanne L Hawley, Jeffrey R PierAbstract:We present the full spectroscopic white Dwarf and hot subDwarf sample from the SDSS first data release, DR1. We find 2551 white Dwarf Stars of various types, 240 hot subDwarf Stars, and an additional 144 objects we have identified as uncertain white Dwarf Stars. Of the white Dwarf Stars, 1888 are non-magnetic DA types and 171, non-magnetic DBs. The remaining (492) objects consist of all different types of white Dwarf Stars: DO, DQ, DC, DH, DZ, hybrid Stars like DAB, etc., and those with non-degenerate companions. We fit the DA and DB spectra with a grid of models to determine the Teff and log(g) for each object. For all objects, we provide coordinates, proper motions, SDSS photometric magnitudes, and enough information to retrieve the spectrum/image from the SDSS public database. This catalog nearly doubles the known sample of spectroscopically-identified white Dwarf Stars. In the DR1 imaged area of the sky, we increase the known sample of white Dwarf Stars by a factor of 8.5. We also comment on several particularly interesting objects in this sample.
D. E. Winget - One of the best experts on this subject based on the ideXlab platform.
-
Exploring the Universe with White Dwarf Stars: The First Year of the Freshman Research Initiative
2010Co-Authors: Michael H. Montgomery, D. E. Winget, A. Allen, Ross E. Falcon, J. Gomez, Jennifer L. Ellis, V. Havanur, K. Luecke, K. Melin, G. F. MillerAbstract:We present results from the first year of the Astronomy Stream of the Freshman Research Initiative at the University of Texas. This program is designed to involve freshmen directly in our research on white Dwarf Stars. We describe the progress the students have made in the last year on (a) planet detection using pulsating white Dwarfs including identifying a promising new candidate, (b) improving our data analysis techniques, (c) updating our web page interface for remote participation, and (d) making preliminary calculations for 3D hydrodynamic modeling of convection in white Dwarf Stars.
-
Limits on planets around pulsating white Dwarf Stars
The Astrophysical Journal, 2008Co-Authors: Fergal Mullally, D. E. Winget, Steven Degennaro, Elizabeth Jeffery, Susan E. Thompson, D. Chandler, Souza Oliveira KeplerAbstract:We present limits on planetary companions to pulsating white Dwarf Stars. A subset of these Stars exhibit extreme stability in the period and phase of some of their pulsation modes; a planet can be detected around such a star by searching for periodic variations in the arrival time of these pulsations. We present limits on companions greater than a few Jupiter masses around a sample of 15 white Dwarf Stars as part of an ongoing survey. One star shows a variation in arrival time consistent with a 2MJ planet in a 4.5 yr orbit. We discuss other possible explanations for the observed signal and conclude that a planet is the most plausible explanation based on the data available.
-
Limits on Planets Around White Dwarf Stars
arXiv: Astrophysics, 2008Co-Authors: Fergal Mullally, D. E. Winget, Steven Degennaro, Elizabeth Jeffery, Susan E. Thompson, D. ChandlerAbstract:We present limits on planetary companions to pulsating white Dwarf Stars. A subset of these Stars exhibit extreme stability in the period and phase of some of their pulsation modes; a planet can be detected around such a star by searching for periodic variations in the arrival time of these pulsations. We present limits on companions greater than a few Jupiter masses around a sample of 15 white Dwarf Stars as part of an on-going survey. One star shows a variation in arrival time consistent with a 2 M_J planet in a 4.5 year orbit. We discuss other possible explanations for the observed signal and conclude that a planet is the most plausible explanation based on the data available.
-
Pulsating White Dwarf Stars and Precision Asteroseismology
Annual Review of Astronomy and Astrophysics, 2008Co-Authors: D. E. Winget, Souza Oliveira KeplerAbstract:Galactic history is written in the white Dwarf Stars. Their surface properties hint at interiors composed of matter under extreme conditions. In the forty years since their discovery, pulsating white Dwarf Stars have moved from side-show curiosities to center stage as important tools for unraveling the deep mysteries of the Universe. Innovative observational techniques and theoretical modeling tools have breathed life into precision asteroseismology. We are just learning to use this powerful tool, confronting theoretical models with observed frequencies and their time rate-of-change. With this tool, we calibrate white Dwarf cosmochronology; we explore equations of state; we measure stellar masses, rotation rates, and nuclear reaction rates; we explore the physics of interior crystallization; we study the structure of the progenitors of Type Ia supernovae, and we test models of dark matter. The white Dwarf pulsations are at once the heartbeat of galactic history and a window into unexplored and exotic physics.
-
Searching for Planets around Pulsating White Dwarf Stars
2006Co-Authors: Fergal Mullally, D. E. Winget, Souza Oliveira KeplerAbstract:We report on our continuing search for planets around pulsating white Dwarf Stars. All Stars with a main sequence mass less than ∼1 M⊙ are expected to become white Dwarf Stars (WDs), so a search for planets around WDs is a search around the evolutionary end point of a wide range of main sequence spectral types. The range of spectral types also means a broad range of main-sequence lifetimes enabling us to probe planet formation rates as a function both of spectral type and Galactic history. We present data for three Stars in our sample and predict the region of mass-orbital separation space explored by monitoring these Stars for just three years.
Scot Kleinman - One of the best experts on this subject based on the ideXlab platform.
-
Discovery of five new massive pulsating white Dwarf Stars
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: B. G. Castanheira, Souza Oliveira Kepler, Atsuko Nitta, Scot Kleinman, Luciano FragaAbstract:Using the SOuthern Astrophysical Research telescope (SOAR) Optical Imager at the SOAR 4.1 m telescope, we report on the discovery of five new massive pulsating white Dwarf Stars. Our results represent an increase of about 20 per cent in the number of massive pulsators. We have detected both short and long periods, low and high amplitude pulsation modes, covering the whole range of the ZZ Ceti instability strip.In this paper, we present a first seismological study of the new massive pulsators based on the few frequencies detected. Our analysis indicates that these Stars have masses higher than average, in agreement with the spectroscopic determinations. In addition, we study for the first time the ensemble properties of the pulsating white Dwarf Stars with masses above 0.8 M ⊙ . We found a bimodal distribution of the main pulsation period with the effective temperature for the massive DAVs, which indicates mode selection mechanisms.
-
New Pulsating DB White Dwarf Stars From The Sloan Digital Sky Survey
The Astrophysical Journal, 2008Co-Authors: Atsuko Nitta, Souza Oliveira Kepler, Fergal Mullally, Jurek Krzesinski, Scot Kleinman, Anjum S. Mukadam, R. E. Nather, Travis S. Metcalfe, Denis J. Sullivan, Susan E. ThompsonAbstract:We are searching for new He atmosphere white Dwarf pulsators (DBVs) based on the newly found white Dwarf Stars from the spectra obtained by the Sloan Digital Sky Survey. DBVs pulsate at hotter temperature ranges than their better known cousins, the H atmosphere white Dwarf pulsators (DAVs or ZZ Ceti Stars). Since the evolution of white Dwarf Stars is characterized by cooling, asteroseismological studies of DBVs give us opportunities to study white Dwarf structure at a different evolutionary stage than the DAVs. The hottest DBVs are thought to have neutrino luminosities exceeding their photon luminosities, a quantity measurable through asteroseismology. Therefore, they can also be used to study neutrino physics in the stellar interior. So far we have discovered nine new DBVs, doubling the number of previously known DBVs. Here we report the new pulsators' light curves and power spectra.
-
A Catalog of Spectroscopically Identified White Dwarf Stars in the First Data Release of the Sloan Digital Sky Survey
The Astrophysical Journal, 2004Co-Authors: Scot Kleinman, Atsuko Nitta, Daniel J. Eisenstein, James Liebert, Hugh C Harris, Jurek Krzesinski, Jeffrey A Munn, Conard C Dahn, Suzanne L Hawley, Jeffrey R PierAbstract:We present the full spectroscopic white Dwarf and hot subDwarf sample from the Sloan Digital Sky Survey (SDSS) first data release, DR1. We find 2551 white Dwarf Stars of various types, 240 hot subDwarf Stars, and an additional 144 objects we have identified as uncertain white Dwarf Stars. Of the white Dwarf Stars, 1888 are nonmagnetic DA types and 171 are nonmagnetic DBs. The remaining (492) objects consist of all different types of white Dwarf Stars: DO, DQ, DC, DH, DZ, hybrid Stars such as DAB, etc., and those with nondegenerate companions. We fit the DA and DB spectra with a grid of models to determine the Teff and log g for each object. For all objects, we provide coordinates, proper motions, SDSS photometric magnitudes, and enough information to retrieve the spectrum/image from the SDSS public database. This catalog nearly doubles the known sample of spectroscopically identified white Dwarf Stars. In the DR1 imaged area of the sky, we increase the known sample of white Dwarf Stars by a factor of 8.5. We also comment on several particularly interesting objects in this sample.
L. G. Althaus - One of the best experts on this subject based on the ideXlab platform.
-
Evolutionary and pulsational properties of white Dwarf Stars
The Astronomy and Astrophysics Review, 2010Co-Authors: L. G. Althaus, A. H. Córsico, Jordi Isern, Enrique García-berroAbstract:White Dwarf Stars are the final evolutionary stage of the vast majority of Stars, including our Sun. Since the coolest white Dwarfs are very old objects, the present population of white Dwarfs contains a wealth of information on the evolution of Stars from birth to death, and on the star formation rate throughout the history of our Galaxy. Thus, the study of white Dwarfs has potential applications in different fields of astrophysics. In particular, white Dwarfs can be used as independent reliable cosmic clocks, and can also provide valuable information about the fundamental parameters of a wide variety of stellar populations, such as our Galaxy and open and globular clusters. In addition, the high densities and temperatures characterizing white Dwarfs allow these Stars to be used as cosmic laboratories for studying physical processes under extreme conditions that cannot be achieved in terrestrial laboratories. Last but not least, since many white Dwarf Stars undergo pulsational instabilities, the study of their properties constitutes a powerful tool for applications beyond stellar astrophysics. In particular, white Dwarfs can be used to constrain fundamental properties of elementary particles such as axions and neutrinos and to study problems related to the variation of fundamental constants. These potential applications of white Dwarfs have led to renewed interest in the calculation of very detailed evolutionary and pulsational models for these Stars. In this work, we review the essentials of the physics of white Dwarf Stars. We enumerate the reasons that make these Stars excellent chronometers, and we describe why white Dwarfs provide tools for a wide variety of applications. Special emphasis is placed on the physical processes that lead to the formation of white Dwarfs as well as on the different energy sources and processes responsible for chemical abundance changes that occur along their evolution. Moreover, in the course of their lives, white Dwarfs cross different pulsational instability strips. The existence of these instability strips provides astronomers with a unique opportunity to peer into their internal structure that would otherwise remain hidden from observers. We will show that this allows one to measure stellar masses with unprecedented precision and to infer their envelope thicknesses, to probe the core chemical stratification, and to detect rotation rates and magnetic fields. Consequently, in this work, we also review the pulsational properties of white Dwarfs and the most recent applications of white Dwarf asteroseismology.
-
evolutionary and pulsational properties of white Dwarf Stars
arXiv: Solar and Stellar Astrophysics, 2010Co-Authors: L. G. Althaus, A. H. Córsico, Jordi Isern, E GarciaberroAbstract:Abridged. White Dwarf Stars are the final evolutionary stage of the vast majority of Stars, including our Sun. The study of white Dwarfs has potential applications to different fields of astrophysics. In particular, they can be used as independent reliable cosmic clocks, and can also provide valuable information about the fundamental parameters of a wide variety of stellar populations, like our Galaxy and open and globular clusters. In addition, the high densities and temperatures characterizing white Dwarfs allow to use these Stars as cosmic laboratories for studying physical processes under extreme conditions that cannot be achieved in terrestrial laboratories. They can be used to constrain fundamental properties of elementary particles such as axions and neutrinos, and to study problems related to the variation of fundamental constants. In this work, we review the essentials of the physics of white Dwarf Stars. Special emphasis is placed on the physical processes that lead to the formation of white Dwarfs as well as on the different energy sources and processes responsible for chemical abundance changes that occur along their evolution. Moreover, in the course of their lives, white Dwarfs cross different pulsational instability strips. The existence of these instability strips provides astronomers with an unique opportunity to peer into their internal structure that would otherwise remain hidden from observers. We will show that this allows to measure with unprecedented precision the stellar masses and to infer their envelope thicknesses, to probe the core chemical stratification, and to detect rotation rates and magnetic fields. Consequently, in this work, we also review the pulsational properties of white Dwarfs and the most recent applications of white Dwarf asteroseismology.
-
Mass-radius relations for massive white Dwarf Stars
Astronomy & Astrophysics, 2005Co-Authors: L. G. Althaus, Enrique García-berro, Jordi Isern, A. H. CórsicoAbstract:We present detailed theoretical mass-radius relations for massive white Dwarf Stars with oxygen-neon cores. This work is motivated by recent observational evidence about the existence of white Dwarf Stars with very high surface gravities. Our results are based on evolutionary calculations that take into account the chemical composition expected from the evolutionary history of massive white Dwarf progenitors. We present theoretical mass-radius relations for stellar mass values ranging from 1.06 to 1.30 Mo with a step of 0.02 Mo and effective temperatures from 150000 K to approx. 5,000 K. A novel aspect predicted by our calculations is that the mass-radius relation for the most massive white Dwarfs exhibits a marked dependence on the neutrino luminosity. Extensive tabulations for massive white Dwarfs, accessible from our web site, are presented as well.
-
Evolution of White Dwarf Stars
Revista Mexicana De Astronomia Y Astrofisica, 2001Co-Authors: L. G. AlthausAbstract:Resumen en: This paper is aimed at presenting the main results we have obtained for the study of the evoution of white Dwarf Stars. The calculations are carried out ...
