Download or read book Evolutionary Models of White Dwarfs with Helium Cores written by and published by . This book was released on 1998 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book White Dwarfs written by G. Vauclair and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 460 pages. Available in PDF, EPUB and Kindle. Book excerpt: The European Workshop on White Dwarfs was initiated by Prof. V. Weidemann, with the first meeting organized in Kiel (FRG) in 1974. Almost every two years, an increasing number of astronomers met to share their results and projects in the subsequent workshops: Frascati (1976), Tel Aviv (1978), Paris (1981), Kiel (1984), Frascati (1986). In the mean time, two major IAU colloquia (No. 53 in Rochester, NY, 1979; and No. 114 in Hanover, NH, 1988) emphasized the importance of these stars for our understanding of stellar evolution. The informal organization of the white dwarf community has been the starting point for large cooperative projects of which the Hubble Space Telescope "White Dwarf Consortium" and the "Whole Earth Telescope" are the most spectacular examples. But many other successful collaborations have also been born during the very exciting discussions conducted in the last 16 years on the occasion of our regular meetings. The 7th European Workshop on White Dwarfs took place the year of the seventieth birthday of Prof. Evry Schatzman, whose pioneering work has been the inspiration for many of the new ideas in the white dwarf community. The Scientific Organizing Committee has agreed to dedicate the workshop to him on this occasion. We are pleased to publish as an introduction to the workshop, the text of the talk delivered by Prof. Schatzman at the workshop's banquet.
Download or read book Observations and Theory of Pulsating Helium White Dwarfs written by Justin D. Steinfadt and published by . This book was released on 2011 with total page 336 pages. Available in PDF, EPUB and Kindle. Book excerpt: Average C/O-core white dwarf stars pulsate in observable normal modes of oscillation with amplitudes of a few percent and periods of 100--1,000 seconds. As of this dissertation, no WD of less than 0.5 Msun has been observed to pulsate. White dwarfs of this low mass likely possess a He core and are products of very different stellar evolution. In this dissertation, we have constructed very low mass He-core WD models and predict the parameter space in which they may be observed to pulsate. We have also observed 13 stars, most of which are He-core WDs, in a search for the first He-core WD pulsator. While we were unsuccessful in discovering a pulsator, our detection limits offer unique constraints on He-core WD pulsation parameter space. As a fortuitous result of our pulsation search, we have discovered two unique eclipsing binary systems. One of these is the first eclipsing detached double white dwarf binary system offering the first opportunity to make model independent constraints on He-core WD models and evolution.
Download or read book Structure and Evolution of Stars written by Martin Schwarzschild and published by Princeton University Press. This book was released on 2015-12-08 with total page 317 pages. Available in PDF, EPUB and Kindle. Book excerpt: With the development of nuclear physics the theory of the stellar interior entered a new phase. Many new investigations have been conducted and the results published in a variety of specialized media. This book brings these results together in a single volume and summarizes the present status of the theory of stellar evolution. Originally published in 1958. The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.
Download or read book Nonradial Oscillations of Stars written by Wasaburō Unno and published by . This book was released on 1989 with total page 442 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Eclipsing White Dwarf Binaries written by S. G. Parsons and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Latest Generation White Dwarf Cooling Models Theory and Applications written by Isabel Renedo Rouco and published by . This book was released on 2015 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt: White dwarfs are the most common stellar evolutionary end-point. Moreover, they can be considered as reliable cosmic clocks to infer the age of a wide variety of stellar populations, including globular and open clusters. Consequently, there is a considerable interest in the study of white dwarf cooling models. In this thesis we used two different approaches. From a theorical perspective, we computed a set of new cooling white dwarfs sequences which incorporates the most up-to-date physical inputs for precision white dwarf cosmochronology and for asteroseismological studies of ZZ Ceti stars. Moreover, we studied the role of 22Ne diffusion in the evolution of white dwarf stars with high-metallicity progenitors. Our evolutionary sequences have been self-consistently evolved from the zero age main sequence to the white dwarf stage. Our calculations include: nuclear burning at the very early phases of white dwarf evolution (which is important to determine the final thickness of the hydrogen-rich envelope), diffusion and gravitational settling (which are important to shape the profiles of the outer layers), accurate neutrino emission rates (which control the cooling at high luminosities), a correct treatment of crystallization and phase separation of carbon and oxygen (which dominate the cooling times at low luminosities), a very detailed equation of state (which is important in all the evolutionary phases), and improved non-gray model atmospheres (which allow for a precise determination of white dwarf colors and outer boundary conditions for the evolving models). From an applied point of view, we use a Monte Carlo simulator that employs our up-to-date evolutionary cooling sequences for white dwarfs. From this and the observations obtained by Hubble Space Telescope of NGC 6791, a nearby metal-rich open cluster, we obtain important conclusions. NGC 6791 is a well studied metal-rich open cluster ([Fe/H]¿ 0.4) that it is so close to us that can be imaged down to luminosities fainter than that of the termination of its white-dwarf cooling sequence, thus allowing for an in-depth study of its white dwarf population. We constrain important properties of this cluster stellar population, such as the age, or the existence of a putative population of massive helium core white dwarfs among other aspects. Some of our main findings can be summarized as follows. With respect to the computation of new cooling sequences for hydrogen-rich DA white dwarfs (Renedo et al. 2010) We correctly reproduced the observed initial-to-final mass relationship of white dwarfs with solar metallicity progenitors. We calculated the energy released from 22Ne sedimentation and we confirm this energy release strongly delays the cooling. The precise value of the delays depends on the mass of the white dwarf, its luminosity and on the metal content. We also solved the age discrepancy between the main sequence turn-off age (̃ 8 Gyr) and the age derived from the termination of the white dwarf cooling sequence (̃ 6 Gyr). Finally we found that the fraction of non-DA white dwarfs in this particular cluster is surprinsingly small, on the order of 6%.
Download or read book Stellar Astrophysics written by Roger John Tayler and published by Taylor & Francis Group. This book was released on 1992 with total page 356 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stellar Astrophysics contains a selection of high-quality papers that illustrate the progress made in research into the structure and evolution of stars. Senior undergraduates, graduates, and researchers can now be brought thoroughly up to date in this exciting and ever-developing branch of astronomy.
Download or read book Pulsations of White Dwarf Stars with Thick Hydrogen Or Helium Surface Layers written by and published by . This book was released on 1986 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to see if there could be agreement between results of stellar evolution theory and those of nonradial pulsation theory, calculations of white dwarf models have been made for hydrogen surface masses of 10−4 solar masses. Earlier results indicated that surface masses greater than 10−8 solar masses would not allow nonradial pulsations, even though all the driving and damping is in surface layers only 10−12 of the mass thick. It is shown that the surface mass of hydrogen in the pulsating white dwarfs (ZZ Ceti variables) can be any value as long as it is thick enough to contain the surface convection zone. 10 refs., 6 figs.
Download or read book White Dwarf Atmospheres and Circumstellar Environments written by Donald W. Hoard and published by John Wiley & Sons. This book was released on 2012-09-19 with total page 342 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written by selected astronomers at the forefront of their fields, this timely and novel book compiles the latest results from research on white dwarf stars, complementing existing literature by focusing on fascinating new developments in our understanding of the atmospheric and circumstellar environments of these stellar remnants. Complete with a thorough refresher on the observational characteristics and physical basis for white dwarf classification, this is a must-have resource for researchers interested in the late stages of stellar evolution, circumstellar dust and nebulae, and the future of our own Solar System.
Download or read book Planets Stars and Stellar Systems written by Linda M. French and published by Springer. This book was released on 2013-02-27 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is volume 3 of Planets, Stars and Stellar Systems, a six-volume compendium of modern astronomical research covering subjects of key interest to the main fields of contemporary astronomy. This volume on “Solar and Stellar Planetary Systems” edited by Linda French and Paul Kalas presents accessible review chapters From Disks to Planets, Dynamical Evolution of Planetary Systems, The Terrestrial Planets, Gas and Ice Giant Interiors, Atmospheres of Jovian Planets, Planetary Magnetospheres, Planetary Rings, An Overview of the Asteroids and Meteorites, Dusty Planetary Systems and Exoplanet Detection Methods. All chapters of the handbook were written by practicing professionals. They include sufficient background material and references to the current literature to allow readers to learn enough about a specialty within astronomy, astrophysics and cosmology to get started on their own practical research projects. In the spirit of the series Stars and Stellar Systems published by Chicago University Press in the 1960s and 1970s, each chapter of Planets, Stars and Stellar Systems can stand on its own as a fundamental review of its respective sub-discipline, and each volume can be used as a textbook or recommended reference work for advanced undergraduate or postgraduate courses. Advanced students and professional astronomers in their roles as both lecturers and researchers will welcome Planets, Stars and Stellar Systems as a comprehensive and pedagogical reference work on astronomy, astrophysics and cosmology.
Download or read book Stellar Structure and Evolution written by Rudolf Kippenhahn and published by Springer Science & Business Media. This book was released on 2012-10-31 with total page 599 pages. Available in PDF, EPUB and Kindle. Book excerpt: This long-awaited second edition of the classical textbook on Stellar Structure and Evolution by Kippenhahn and Weigert is a thoroughly revised version of the original text. Taking into account modern observational constraints as well as additional physical effects such as mass loss and diffusion, Achim Weiss and Rudolf Kippenhahn have succeeded in bringing the book up to the state-of-the-art with respect to both the presentation of stellar physics and the presentation and interpretation of current sophisticated stellar models. The well-received and proven pedagogical approach of the first edition has been retained. The book provides a comprehensive treatment of the physics of the stellar interior and the underlying fundamental processes and parameters. The models developed to explain the stability, dynamics and evolution of the stars are presented and great care is taken to detail the various stages in a star’s life. Just as the first edition, which remained a standard work for more than 20 years after its first publication, the second edition will be of lasting value not only for students but also for active researchers in astronomy and astrophysics.
Download or read book The Evolution of Helium White Dwarfs written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Behavior of Hydrogen and Helium at White Dwarf Photosphere Conditions written by Marc-Andre Schaeuble and published by . This book was released on 2018 with total page 466 pages. Available in PDF, EPUB and Kindle. Book excerpt: White Dwarfs (WDs) represent the evolutionary endpoint for nearly all stars in the universe. Their atmospheres are usually dominated by either hydrogen, helium, or carbon. In astrophysics, WDs are used to determine the age of the universe, to test current stellar evolutionary models, and to constrain the physics of Type Ia supernovae as well as dark energy. Accurate WD masses are needed for all of these applications. In this thesis, I review the weaknesses of the currently available WD mass determination methods and show that for hydrogen-dominated WDs, such deficiencies can be traced to an incomplete understanding of H line shapes at the atmospheric temperaturesand densities (T [subscript e] ~ 1 eV, n [subscript e] ~ 1x1017 cm−3) of those stars. I further demonstrate that helium WD mass derivation techniques suffer from uncertain Stark shift and neutral broadening models, while C WD masses are suspect due to unverified electron broadening parameters. Addressing each of these atomic physics limitations requires both experimental data and theoretical developments. The White Dwarf Photosphere Experiment (WDPE) at Sandia National Laboratories Z-machine delivers laboratory data directed at solving the mass determination problems for WDs. For hydrogen line shapes, I find that fundamental assumptions regarding emission and absorption processes may not be valid. Helium WD mass derivations are hampered by the inability of current models to reproduce my experimental He shift and neutral broadening measurements. Since C WDs are at higher temperatures than H or He WDs, these investigations are limited to proof-of concept experiments. All my WDPE results have led to additional questions about fundamental physical assumptions that are relevant not only to stellar atmospheres and the experimental platform, but all of plasma physics. I discuss each of these aspects in the context of atomic, plasma, and WD physics
Download or read book Stellar Evolution written by Steff Jaywan and published by Dedona Publishing. This book was released on with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stellar evolution refers to the process by which a star changes over the course of time. This field of astrophysics studies the formation, life, and death of stars, which involves a series of complex physical processes and transformations. Here, we outline the key stages and concepts in stellar evolution. Stars form from giant molecular clouds, regions rich in gas and dust. Under the influence of gravity, these clouds collapse and fragment, leading to the formation of dense cores. When a core reaches a critical density, nuclear fusion ignites in its center, giving birth to a protostar. Once nuclear fusion stabilizes, converting hydrogen into helium in the core, the star enters the main sequence phase. This is the longest stage in a star's life, where it remains in hydrostatic equilibrium, with gravitational forces balanced by radiation pressure from fusion. The duration of this phase depends on the star's mass. Low-mass stars, such as red dwarfs, can remain on the main sequence for tens to hundreds of billions of years. Intermediate-mass stars, like our Sun, stay on the main sequence for about 10 billion years. High-mass stars, such as blue giants, have much shorter main sequence lifespans, ranging from a few million to tens of millions of years.
Download or read book On the Spectral Evolution of Cool Helium Atmosphere White Dwarfs Detailed Spectroscopic and Photometric Analysis of DZ Stars written by and published by . This book was released on 2007 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present a detailed analysis of a large spectroscopic and photometric sample of DZ white dwarfs based on our latest model atmosphere calculations. We revise the atmospheric parameters of the trigonometric parallax sample of Bergeron, Leggett, & Ruiz (12 stars) and analyze 147 new DZ white dwarfs discovered in the SDSS. The inclusion of metals and hydrogen in our model atmosphere calculations leads to different atmospheric parameters than those derived from pure helium models. Calcium abundances are found in the range from log (Ca/He) = -12 to -8. We also find that fits of the coolest objects show peculiarities, suggesting that our physical models may not correctly describe the conditions of high atmospheric pressure encountered in the coolest DZ stars. We find that the mean mass of the 11 DZ stars with trigonometric parallaxes is significantly lower than that obtained from pure helium models and in much better agreement with the mean mass of other types of white dwarfs. We determine hydrogen abundances for 27% of the DZ stars in our sample, while only upper limits are obtained for objects with low-S/N spectroscopic data. We confirm with a high level of confidence that the accretion rate of hydrogen is at least 2 orders of magnitude smaller than that of metals (and up to 5 in some cases) to be compatible with the observations. We find a correlation between the hydrogen abundance and the effective temperature, suggesting for the first time empirical evidence of a lower temperature boundary for the hydrogen screening mechanism. Finally, we speculate on the possibility that the DZA white dwarfs could be the result of the convective mixing of thin hydrogen rich atmospheres with the underlying helium convection zone.
Download or read book 15th European Workshop on White Dwarfs written by Ralf Napiwotzki and published by . This book was released on 2007 with total page 718 pages. Available in PDF, EPUB and Kindle. Book excerpt:
