Topic
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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TL;DR: In this article, a review of the observations that bear most directly on the structure of cataclysmic variables at minimum light are reviewed. Sections include: the basic model, masses, the structures of the disk, the rapid oscillations, and the source of the eruptions.
Abstract: The cataclysmic variables are usually divided into the following four classes: novae; recurrent novae; dwarf novae, which are subclassified as U Geminorum stars or Z Camelopardalis stars; and novalike variables. Those observations that bear most directly on the structure of cataclysmic variables at minimum light are reviewed. Sections include: the basic model; masses; the structure of the disk; the rapid oscillations; and the source of the eruptions. 5 figs., 4 tables, 133 refs. (GHT)
117 citations
TL;DR: In this paper, the authors reported the spectroscopic confirmation of four further white dwarf members of Praesepe, bringing the total number of confirmed white dwarf me mbers to eleven making this the second largest collection of these objects in an open clu ster identified to date.
Abstract: We report the spectroscopic confirmation of four further whi te dwarf members of Praesepe. This brings the total number of confirmed white dwarf me mbers to eleven making this the second largest collection of these objects in an open clu ster identified to date. This number is consistent with the high mass end of the initial mass function of Praesepe being Salpeter in form. Furthermore, it suggests that the bulk of Praesepe white dwarfs did not gain a substantial recoil kick velocity from possible asymmetries in thei r loss of mass during the asymptotic giant branch phase of evolution. By comparing our estimates of the effective temperatures and the surface gravities of WD0833+194, WD0840+190, WD0840+205 and WD0843+184 to modern theoretical evolutionary tracks we have derived their masses to be in the range 0.72 0.76M⊙ and their cooling ages �300Myrs. For an assumed cluster age of 625±50Myrs the infered progenitor masses are between 3.3 3.5M⊙. Examining these new data in the context of the initial mass-final mass relation we find that it can be adequately represented by a linear function (a0=0.289±0.051, a1=0.133±0.015) over the initial mass range 2.7M⊙ to 6M⊙. Assuming an extrapolation of this relation to larger initi al masses is valid and adopting a maximum white dwarf mass of 1.3M⊙, our results support a minimum mass for core-collapse supernovae progenitors in the range �6.8-8.6M⊙.
116 citations
TL;DR: In this article, the effect of the instability of the accretion disc on the evolution of white dwarf (WD) binaries was considered, and the initial parameters for SNe Ia in the orbital period secondary mass (log P(i) - M(2)(i)) plane for various WD masses for these two channels, respectively.
Abstract: The nature of the progenitors of Type Ia supernovae (SNe Ia) is still unclear. In this paper, by considering the effect of the instability of accretion disc on the evolution of white dwarf (WD) binaries, we performed binary evolution calculations for about 2400 close WD binaries, in which a carbon-oxygen WD accretes material from a main-sequence (MS) star or a slightly evolved subgiant star (WD + MS channel), or a red-giant star (WD + RG channel) to increase its mass to the Chandrasekhar (Ch) mass limit. According to these calculations, we mapped out the initial parameters for SNe Ia in the orbital period-secondary mass (log P(i) - M(2)(i)) plane for various WD masses for these two channels, respectively. We confirm that WDs in the WD + MS channel with a mass as low as 0.61 M(circle dot) can accrete efficiently and reach the Ch limit, while the lowest WD mass for the WD + RG channel is 1.0 M(circle dot). We have implemented these results in a binary population synthesis study to obtain the SN Ia birthrates and the evolution of SN Ia birthrates with time for both a constant star formation rate and a single starburst. We find that the Galactic SN Ia birthrate from the WD + MS channel is similar to 1.8 x 10(-3) yr(-1) according to our standard model, which is higher than the previous results. However, similar to the previous studies, the birthrate from the WD + RG channel is still low (similar to 3 x 10(-5) yr(-1)). We also find that about one-third of SNe Ia from the WD + MS channel and all SNe Ia from the WD + RG channel can contribute to the old populations (greater than or similar to 1 Gyr) of SN Ia progenitors.
116 citations
TL;DR: In this article, a detailed analysis of all the known hot DQ white dwarfs in the Fourth Data Release of the Sloan Digital Sky Survey (SDSS) recently found to have carbon-dominated atmospheres is presented.
Abstract: We present a detailed analysis of all the known hot DQ white dwarfs in the Fourth Data Release of the Sloan Digital Sky Survey (SDSS) recently found to have carbon-dominated atmospheres. Our spectroscopic and photometric analysis reveals that these objects all have effective temperatures between ~18,000 and 24,000 K. The surface composition is found to be completely dominated by carbon, as revealed by the absence of H? and He I ?4471 lines (or a determination of trace amounts in a few cases). We find that the surface gravity of all objects but one seems to be normal and around -->log g = 8.0, while one is likely near -->log g = 9.0. The presence of a weak magnetic field is directly detected by spectropolarimetry in one object and is suspected in two others. We propose that these strange stars could be cooled-down versions of the weird PG 1159 star H1504+65 and form a new family of hydrogen- and helium-deficient objects following the post-AGB phase. Finally, we present the results of full nonadiabatic calculations dedicated specifically to each of the hot DQs that show that only SDSS J142625.70+575218.4 is expected to exhibit luminosity variations. This result is in excellent agreement with recent observations by Montgomery et al., who find that J142625.70+575218.4 is the only pulsator among six hot DQ white dwarfs surveyed in 2008 February.
116 citations
TL;DR: In this paper, the radio observations of 27 Type Ia supernovae (SNe Ia), observed over two decades with the Very Large Array, were discussed and 2 σ upper limits to a steady mass-loss rate for individual SN systems as low as 3 × 10^(-8) M_☉ yr^(-1) were derived.
Abstract: We present and discuss the radio observations of 27 Type Ia supernovae (SNe Ia), observed over two decades with the Very Large Array. No SN Ia has been detected so far in the radio, implying a very low density for any possible circumstellar material established by the progenitor, or progenitor system, before explosion. We derive 2 σ upper limits to a steady mass-loss rate for individual SN systems as low as ~3 × 10^(-8) M_☉ yr^(-1), which argues strongly against white dwarf accretion via a stellar wind from a massive binary companion in the symbiotic star, an example of the "single-degenerate" scenario. However, a white dwarf accreting from a relatively low mass companion via a sufficiently high efficiency (>60%-80%) Roche lobe overflow is still consistent with our limits. The "double-degenerate" merger scenario also cannot be excluded.
116 citations