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White dwarf

About: White dwarf is a research topic. Over the lifetime, 15004 publications have been published within this topic receiving 430597 citations. The topic is also known as: degenerate dwarf.


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Journal ArticleDOI
TL;DR: In this article, the authors study the late evolution of solar metallicity stars in the transition region between white dwarf formation and core collapse, and find that the initial mass range for SAGB evolution is -->7.5-9.25 M
Abstract: We study the late evolution of solar metallicity stars in the transition region between white dwarf formation and core collapse. This includes the super-asymptotic giant branch (super-AGB, SAGB) stars, which ignite carbon burning and form an oxygen-neon (ONe) core. SAGB star cores may grow to the Chandrasekhar mass because of continued H- and He-shell burning, ending as core-collapse supernovae. From stellar evolution models we find that the initial mass range for SAGB evolution is -->7.5–9.25 M☉. We perform calculations with three different stellar evolution codes to judge the robustness of our results. The mass range significantly depends on the treatment of semiconvective mixing and convective overshooting. To consider the effect of a large number of thermal pulses, as expected in SAGB stars, we construct synthetic SAGB models that are calibrated through stellar evolution simulations. The synthetic model enables us to compute the evolution of the main properties of SAGB stars from the onset of thermal pulses until the core reaches the Chandrasekhar mass or is uncovered by the stellar wind. Thereby, we differentiate the stellar initial mass ranges that produce ONe WDs from that leading to electron-capture SNe. The latter is found to be -->9.0–9.25 M☉ for our fiducial model, implying that electron-capture SNe would constitute about 4% of all SNe in the local universe. The error in this determination due to uncertainties in the third dredge-up efficiency and AGB mass-loss rate could lead to about a doubling of the number of electron-capture SNe, which provides a firm upper limit to their contribution to all supernovae of ~20%.

311 citations

Journal ArticleDOI
TL;DR: In this paper, photometric and spectroscopic observations of 110 cool white dwarf stars are presented and analyzed with state-of-the-art model atmosphere calculations appropriate for pure hydrogen and pure helium, as well as mixed H/He compositions.
Abstract: Photometric and spectroscopic observations of 110 cool white dwarf stars are presented and analyzed with state-of-the-art model atmosphere calculations appropriate for cool white dwarfs with pure hydrogen and pure helium, as well as mixed H/He compositions. High signal-to-noise spectroscopy reveals the presence of Hα in 20 white dwarfs previously classified as DC stars, four of which are magnetic. Cool white dwarfs are shown to form a narrow sequence in both color-color and color-magnitude diagrams, with little evidence for separation between hydrogen- and helium-rich compositions in these diagrams. The observed energy distributions are obtained from a combination of both optical BVRI and infrared JHK photometric data and used to derive both the effective temperature and the atmospheric composition of each star. Stellar masses are also obtained for 60 white dwarfs with known trigonometric parallaxes. Some discrepancies between the observed energy distributions and those predicted by the model atmospheres are described. In particular, evidence for the presence of a UV opacity source in the coolest hydrogen-rich white dwarfs is interpreted in terms of a pseudo continuum opacity originating from the Lyman edge. The simultaneous analysis of the photometric and spectroscopic observations provides a detailed picture of the chemical composition of cool white dwarfs. Most cool white dwarfs have energy distributions that are well reproduced by either pure hydrogen or pure helium models, with little evidence for objects with mixed atmospheric compositions. We identify a peculiar class of non-DA star with Teff > 6000 K whose energy distributions are well reproduced by pure hydrogen models but whose spectra do not show Hα. Our results reveal an inhomogeneous temperature distribution of hydrogen- and helium-rich white dwarfs, and in particular the presence of a non-DA gap in the range 5000 Teff 6000 K. The chemical evolution of cool white dwarfs is discussed at length with respect to our findings. We show that no known physical mechanisms (e.g., convective mixing, convective dredge-up, accretion from the interstellar medium) can account for the temperature distribution of hydrogen- and helium-rich white dwarfs. Possible new mechanisms that could explain our results are presented. We propose a mechanism by which hydrogen is accreted onto the surface of helium-rich white dwarfs while remaining spectroscopically invisible. Observational evidence that supports our hypothesis is discussed. Lower limits for the age of the local Galactic disk are obtained by determining the age of the oldest white dwarfs in our sample. Ages in the range 6.5-10 Gyr are derived from evolutionary models with various core compositions and helium envelope masses.

311 citations

Journal ArticleDOI
TL;DR: In this article, atmospheric pollution by various elements heavier than helium has been used to infer that a comparable fraction of the white dwarf descendants of such main-sequence stars are orbited by planetary systems, and for plausible planetary system configurations, this total mass is likely to be at least equal to that of the Sun's asteroid belt.
Abstract: Infrared studies have revealed debris likely related to planet formation in orbit around ~30% of youthful, intermediate mass, main-sequence stars. We present evidence, based on atmospheric pollution by various elements heavier than helium, that a comparable fraction of the white dwarf descendants of such main-sequence stars are orbited by planetary systems. These systems have survived, at least in part, through all stages of stellar evolution that precede the white dwarf. During the time interval (~200 million years) that a typical polluted white dwarf in our sample has been cooling it has accreted from its planetary system the mass of one of the largest asteroids in our solar system (e.g., Vesta or Ceres). Usually, this accreted mass will be only a fraction of the total mass of rocky material that orbits these white dwarfs; for plausible planetary system configurations we estimate that this total mass is likely to be at least equal to that of the Sun's asteroid belt, and perhaps much larger. We report abundances of a suite of eight elements detected in the little studied star G241-6 that we find to be among the most heavily polluted of all moderately bright white dwarfs.

308 citations

01 Dec 2005
TL;DR: In this article, four ground-based photometric systems with respect to the Hubble Space Telescope (HST) absolute flux scale, defined by Vega and four fundamental DA white dwarfs, are compared with the respective observed magnitudes of larger sets of DA white stars that have well-determined effective temperatures and surface gravities.
Abstract: We have calibrated four major ground-based photometric systems with respect to the Hubble Space Telescope (HST) absolute flux scale, which is defined by Vega and four fundamental DA white dwarfs. These photometric systems include the Johnson-Kron-Cousins UBVRI, the Stromgren uvby filters, the Two Micron All Sky Survey JHKs, and the Sloan Digital Sky Survey ugriz filters. Synthetic magnitudes are calculated from model white dwarf spectra folded through the published filter response functions; these magnitudes in turn are absolutely calibrated with respect to the HST flux scale. Effective zero-magnitude fluxes and zero-point offsets of each system are determined. In order to verify the external observational consistency, as well as to demonstrate the applicability of these definitions, the synthetic magnitudes are compared with the respective observed magnitudes of larger sets of DA white dwarfs that have well-determined effective temperatures and surface gravities and span a wide range in both of these parameters.

307 citations

Journal ArticleDOI
TL;DR: In this article, the influence of the initial composition of the exploding white dwarf on the nucleosynthesis, light curves and spectra of Type Ia supernovae has been studied in order to evaluate the size of evolutionary effects on cosmological time scales.
Abstract: The influence of the initial composition of the exploding white dwarf on the nucleosynthesis, light curves and spectra of Type Ia supernovae has been studied in order to evaluate the size of evolutionary effects on cosmological time scales, how the effects can be recognized and how one may be able to correct for them. The calculations are based on a set of delayed detonation models which give a good account of the optical and infrared light curves and of the spectral evolution. The explosions and light curves are calculated using a one- dimensional Lagrangian radiation-hydro code including a nuclear network. NLTE- spectra are computed for various epochs using the structure resulting from the light curve code. The following questions are addressed : What do we learn about the progenitor evolution and its metallicity? What are the systematic effects for the determination of the cosmological parameters $\Omega_M$ and $\Lambda$ and how can we recognize this potential 'pitfalls' and correct for evolutionary effects?

300 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023367
2022667
2021495
2020557
2019548
2018515