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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: A series of radial velocity observations has been obtained over the last 3 years of a sample of 20 Ba II stars as discussed by the authors, and they were found to show long-term velocity variations ranging in amplitude from a few to tens of km s/sup -1.
Abstract: A series of radial velocity observations has been obtained over the last 3 years of a sample of 20 Ba II stars. Seventeen of these (85%) are found to show long-term velocity variations ranging in amplitude from a few to tens of km s/sup -1/. Thus it seems likely that all Ba II stars are binary systems. An additional Ba II star in the open cluster NGC 2420 is also found to have a variable velocity. Orbits for seven Ba II stars indicate low-mass companions, compatible with their being white dwarfs. Separations are large, about 2 AU on average. The peculiar abundances are not explained, but the fact remains that multiplicity must bear a causal relationship to these peculiarities.

132 citations

Journal ArticleDOI
06 Mar 2015-Science
TL;DR: A spectroscopic and kinematic analysis of US 708, the fastest unbound star in the authors' Galaxy, finds that it is a fast rotator and according to the binary evolution model, it was spun-up by tidal interaction in a close binary and is likely to be the ejected donor remnant of a thermonuclear supernova.
Abstract: Hypervelocity stars (HVSs) travel with velocities so high that they exceed the escape velocity of the Galaxy. Several acceleration mechanisms have been discussed. Only one HVS (US 708, HVS 2) is a compact helium star. Here we present a spectroscopic and kinematic analysis of US 708. Traveling with a velocity of ~1200 kilometers per second, it is the fastest unbound star in our Galaxy. In reconstructing its trajectory, the Galactic center becomes very unlikely as an origin, which is hardly consistent with the most favored ejection mechanism for the other HVSs. Furthermore, we detected that US 708 is a fast rotator. According to our binary evolution model, it was spun-up by tidal interaction in a close binary and is likely to be the ejected donor remnant of a thermonuclear supernova.

132 citations

01 Dec 1996
TL;DR: In this paper, the authors derived the critical size of the mixed region required to initiate a detonation in a degenerate carbon-oxygen mixture and showed that this critical region is much larger than the width of the reaction front of a Chapman-Jouguet detonation.
Abstract: We derive the criteria for deflagration to detonation transition (DDT) in a Type Ia supernova. The theory is based on two major assumptions: (1) detonation is triggered via the Zeldovich gradient mechanism inside a region of mixed fuel and products, and (2) the mixed region is produced by a turbulent mixing of fuel and products either inside an active deflagration front or during the global expansion and subsequent contraction of an exploding white dwarf. We determine the critical size of the mixed region required to initiate a detonation in a degenerate carbon-oxygen mixture. This critical length is much larger than the width of the reaction front of a Chapman-Jouguet detonation. However, at densities greater than 5 × 106 g cm-3, it is much smaller than the size of a white dwarf. We derive the critical turbulent intensity required to create the mixed region inside an active deflagration front in which a detonation can form. We conclude that the density ρtr at which a detonation can form in a carbon-oxygen white dwarf is low, less than 2-5 × 107 g cm-3 but greater than 5 × 106 g cm-3.

131 citations

Journal ArticleDOI
TL;DR: In this article, the authors present observations of four rapidly rising (trise ≈ 10 days) transients with peak luminosities between those of supernovae (SNe) and superluminous SNe (Mpeak ap; -20) -one discovered and followed by the Palomar Transient Factory (PTF) and three by the Supernova Legacy Survey.
Abstract: The American Astronomical Society. All rights reserved..We present observations of four rapidly rising (trise ≈ 10 days) transients with peak luminosities between those of supernovae (SNe) and superluminous SNe (Mpeak ap; -20) - one discovered and followed by the Palomar Transient Factory (PTF) and three by the Supernova Legacy Survey. The light curves resemble those of SN 2011kl, recently shown to be associated with an ultra-long-duration gamma-ray burst (GRB), though no GRB was seen to accompany our SNe. The rapid rise to a luminous peak places these events in a unique part of SN phase space, challenging standard SN emission mechanisms. Spectra of the PTF event formally classify it as an SN II due to broad Hα emission, but an unusual absorption feature, which can be interpreted as either high velocity Hα (though deeper than in previously known cases) or Si ii (as seen in SNe Ia), is also observed. We find that existing models of white dwarf detonations, CSM interaction, shock breakout in a wind (or steeper CSM), and magnetar spin down cannot readily explain the observations. We consider the possibility that a "Type 1.5 SN" scenario could be the origin of our events. More detailed models for these kinds of transients and more constraining observations of future such events should help to better determine their nature. © 2016.

131 citations


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