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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
22 Nov 2007-Nature
TL;DR: The analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution, although these objects might be the cooler counterpart of the unique and extensively studied PG 1159 star H1504+65.
Abstract: White dwarf stars are an endpoint of stellar evolution for some smaller stars. They come in two forms as a rule, with either hydrogen- or helium-rich atmospheres. The discovery of white dwarfs with atmospheres primarily composed of carbon, with little or no hydrogen or helium, is therefore unexpected. Though quite rare, this new type of star appears to represent an alternative route for stellar evolution. The discovery of several white dwarfs with atmospheres primarily composed of carbon, with little or no trace of hydrogen or helium is reported. These stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution. White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 and 8–10 , where is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is surrounded by a helium layer and, for ∼80 per cent of known white dwarfs, by an additional hydrogen layer1,2,3. All white dwarfs therefore have been traditionally found to belong to one of two categories: those with a hydrogen-rich atmosphere (the DA spectral type) and those with a helium-rich atmosphere (the non-DAs). Here we report the discovery of several white dwarfs with atmospheres primarily composed of carbon, with little or no trace of hydrogen or helium. Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution, although these objects might be the cooler counterpart of the unique and extensively studied PG 1159 star H1504+65 (refs 4–7). These stars, together with H1504+65, might accordingly form a new evolutionary sequence that follows the asymptotic giant branch.

148 citations

Journal ArticleDOI
TL;DR: In this article, a steady-state thin accretion disk is modeled around a uniformly rotating unmagnetized star in order to investigate whether disk accretion can continue as the accreted angular momentum spins the central star to near breakup.
Abstract: A steady-state thin accretion disk is modeled around a uniformly rotating unmagnetized star in order to investigate whether disk accretion can continue as the accreted angular momentum spins the central star to near breakup. A mapping between the specific angular momentum (SAM) added to the star and the stellar rotation rate (SRR) is obtained. When SRR is somewhat less than the breakup rotation rate of the star, a class of solutions is found where the angular velocity of the disk attains a maximum close to the star and then decreases rapidly in a boundary layer to match SRR. If SRR is near breakup, a second class of solutions is found where the disk angular velocity has no maximum but increases monotonically all the way down to the stellar surface. SAM decreases very rapidly with increasing SRR and even takes on fairly large negative values. The spin-up of an accreting star slows down and eventually stops at a rotation rate near breakup. Beyond this point, the star can continue to accrete any amount of matter without actually breaking up. 18 refs.

148 citations

Journal ArticleDOI
TL;DR: In this article, the authors calculated diffusion timescales for Ca, Mg, Fe in hydrogen atmosphere white dwarfs with temperatures between 5000 and 25 000 K and determined accretion rates with the Bondi-Hoyle formula for hydrodynamic accretion.
Abstract: We calculated diffusion timescales for Ca, Mg, Fe in hydrogen atmosphere white dwarfs with temperatures between 5000 and 25 000 K. With these timescales we determined accretion rates for a sample of 38 DAZ white dwarfs from the recent studies of Zuckerman et al. (2003, ApJ, 596, 477) and Koester et al. (2005, A&A, 432, 1025). Assuming that the accretion rates can be calculated with the Bondi-Hoyle formula for hydrodynamic accretion, we obtained estimates for the interstellar matter density around the accreting objects. These densities are in good agreement with new data about the warm, partially ionized phase of the ISM in the solar neighborhood.

148 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented new determinations of effective temperature, surface gravity, and masses for a sample of 46 hot DA white dwarfs selected from the Extreme Ultraviolet Explorer (EUVE) and ROSAT Wide Field Camera bright source lists in the course of a near-infrared survey for low-mass companions.
Abstract: We present new determinations of effective temperature, surface gravity, and masses for a sample of 46 hot DA white dwarfs selected from the Extreme Ultraviolet Explorer (EUVE) and ROSAT Wide Field Camera bright source lists in the course of a near-infrared survey for low-mass companions. Our analysis, based on hydrogen non-LTE model atmospheres, provides a map of LTE correction vectors, which allow a thorough comparison with previous LTE studies. We find that previous studies underestimate both the systematic errors and the observational scatter in the determination of white dwarf parameters obtained via fits to model atmospheres. The structure of very hot or low-mass white dwarfs depends sensitively on their history. To compute white dwarf masses, we thus use theoretical mass-radius relations that take into account the complete evolution from the main sequence. We find a peak mass of our white dwarf sample of 0.59 M☉, in agreement with the results of previous analyses. However, we do not confirm a trend of peak mass with temperature reported in two previous analyses. Analogous to other EUV-selected samples, we note a lack of low-mass white dwarfs and a large fraction of massive white dwarfs. Only one white dwarf is likely to have a helium core. While the lack of helium white dwarfs in our sample can be easily understood from their high cooling rate, and therefore low detection probability in our temperature range, this is not enough to explain the large fraction of massive white dwarfs. This feature very likely results from a decreased relative sample volume for low-mass white dwarfs caused by interstellar absorption in EUV-selected samples.

148 citations


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