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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 discuss the targeted search for hypervelocity stars (HVSs), stars traveling with velocities so extreme that dynamical ejection from a massive black hole is their only suggested origin.
Abstract: We discuss our targeted search for hypervelocity stars (HVSs), stars traveling with velocities so extreme that dynamical ejection from a massive black hole is their only suggested origin. Our survey, now half-complete, has successfully identified a total of four probable HVSs plus a number of other unusual objects. Here we report the two most recently discovered HVSs: SDSS J110557.45+093439.5 and possibly SDSS J113312.12+010824, traveling with Galactic rest-frame velocities at least +508 ± 12 and +418 ± 10 km s-1, respectively. The other late B-type objects in our survey are consistent with a population of post-main-sequence stars or blue stragglers in the Galactic halo, with mean metallicity [Fe/H] = -1.3 and velocity dispersion 108 ± 5 km s-1. It is interesting to note that the velocity distribution shows a tail of objects with large positive velocities that may be a mix of low-velocity HVSs and high-velocity runaway stars. Our survey also includes a number of DA white dwarfs with unusually red colors, possibly extremely low mass objects. Two of our objects are B supergiants in the Leo A dwarf, providing the first spectroscopic evidence for star formation in this dwarf galaxy within the last ~30 Myr.

135 citations

Journal ArticleDOI
TL;DR: In this article, the authors examined three sets of assumptions concerning the distribution of debris material between a disc and a corona, and showed that a model comprising both fast accretion to form a (hot) corona andslow accretion from a (cold) debris disc can reproduce the observed distribution of helium-rich subdwarfs in terms of their surface temperatures, gravities, nitrogen and carbon.
Abstract: Recentsurveyshavedemonstratedtheexistenceofseveralshort-periodbinarysystemscontaining two white dwarfs. Following orbital decay by gravitational-wave radiation, such binaries are expected to merge at a rate of two or three per thousand years per galaxy. The consequences of such a merger depend on the individual white dwarf masses, but are believed to include helium-rich subdwarfs, RCrB stars, extreme helium stars and also AMCVn systems and possibly Type Ia supernovae. Whilst the hydrodynamics of the merger process remains difficult to compute, it is possible to compute the evolution of a double white dwarf merger following the destruction of one component. In this paper, we describe the evolution following the merger of two helium white dwarfs. We examine three sets of assumptions concerning the distribution of debris material between a disc and a corona. Our results demonstrate that a model comprising both fast accretion to form a (hot) corona andslow accretion from a (cold) debris disc can reproduce the observed distribution of helium-rich subdwarfs in terms of their surface temperatures, gravities, nitrogen and carbon

135 citations

Journal ArticleDOI
TL;DR: In this paper, the Caltech-Parkes-Swinburne Recorder II was used to estimate the mass of the binary millisecond pulsar PSR J1909-3744.
Abstract: We report on nearly 2 years of timing observations of the low-mass binary millisecond pulsar PSR J1909-3744 with the Caltech-Parkes-Swinburne Recorder II, a new instrument that gives unprecedented timing precision. Daily observations give a weighted rms residual of 74 ns, indicating an extremely low level of systematic error. We have greatly improved on the previous parallax and proper motion measurements of PSR J1909-3744, yielding a distance of 1.14 kpc and transverse velocity of 200 km s-1. The system's orbital eccentricity is just (1.35 ± 12) × 10-7, the smallest yet recorded. Since their discovery, the masses of the rapidly rotating millisecond pulsars have remained a mystery, with the recycling hypothesis arguing for heavy objects, and the accretion-induced collapse of a white dwarf more consistent with neutron stars less than the Chandrashkar limit. Fortuitously, PSR J1909-3744 is an edge-on system, and our data have allowed the measurement of the range and shape of the Shapiro delay to high accuracy, giving the first precise determination of a millisecond pulsar mass to date, mp = 1.438 ± 0.024 M☉. The mass of PSR J1909-3744 is at the upper edge of the range observed in mildly recycled pulsars in double neutron star systems, consistent with the recycling hypothesis. It appears that the production of millisecond pulsars is possible with the accretion of <0.2 M☉.

135 citations

Journal ArticleDOI
TL;DR: In this article, a detailed analysis of 101 white dwarf main-sequence binaries (WDMS) from the Sloan Digital Sky Survey (SDSS) for which multiple SDSS spectra are available is presented.
Abstract: We present a detailed analysis of 101 white dwarf main-sequence binaries (WDMS) from the Sloan Digital Sky Survey (SDSS) for which multiple SDSS spectra are available. We detect significant radial velocity variations in 18 WDMS, identifying them as post-common-envelope binaries (PCEBs) or strong PCEB candidates. Strict upper limits to the orbital periods are calculated, ranging from 0.43 to 7880 d. Given the sparse temporal sampling and relatively low spectral resolution of the SDSS spectra, our results imply a PCEB fraction of greater than or similar to 15 per cent among the WDMS in the SDSS data base. Using a spectral decomposition/fitting technique we determined the white dwarf effective temperatures and surface gravities, masses and secondary star spectral types for all WDMS in our sample. Two independent distance estimates are obtained from the flux-scaling factors between the WDMS spectra, and the white dwarf models and main-sequence star templates, respectively. Approximately one-third of the systems in our sample show a significant discrepancy between the two distance estimates. In the majority of discrepant cases, the distance estimate based on the secondary star is too large. A possible explanation for this behaviour is that the secondary star spectral types that we determined from the SDSS spectra are systematically too early by one to two spectral classes. This behaviour could be explained by stellar activity, if covering a significant fraction of the star by cool dark spots will raise the temperature of the interspot regions. Finally, we discuss the selection effects of the WDMS sample provided by the SDSS project.

134 citations


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