Journal ArticleDOI
Double white dwarfs as progenitors of R Coronae Borealis stars and type I supernovae
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TLDR
In this article, the authors explored the role of mass transfer in the evolution of double degenerate systems and found that low-mass helium/helium pairs are unstable to dynamical time-scale mass transfer and probably coalesce to form helium-burning sdO stars.Abstract:
Close double white dwarfs should arise from the second phase of mass exchagne in close binaries which first encountered mass exchange while the more massive star was crossing the Hertzprung gap. Tidal mass transfer in these double degenerate systems is explored. The sequence of double white dwarf divides naturally into three segments. (1) Low-mass helium/helium pairs are unstable to dynamical time-scale mass transfer and probably coalesce to form helium-burning sdO stars. (2) In helium/carbon-oxygen pairs, mass transfer occurs on the time scale for gravitational radiation losses (approx.10/sup -4/ M/sub sun/ yr/sup -1/); the accreted helium is quickly ignited, and the accretor expands to dimensions characteristic of R CrB stars, engulfing its companion star. (3) Carbon-oxygen/carbon-oxygen pairs are again unstable to dynamical time-scale mass transfer and, since their total masses exceed the Chandrasekhar limit, are destined to become supernovae. Inactive lifetimes in these latter systems between creation and interaction can exceed 10/sup 10/ years. Birthrates of R CrB stars and Type I supernovae by evolution of double white dwarfs are in reasonable agreement with observational estimates.read more
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Journal ArticleDOI
The R Coronae Borealis Stars - A Few Mere Facts
TL;DR: In this paper, an abundance analysis of a complete sample (18 stars) of the warm galactic R Coronae Borealis (RCB) variables has been performed and the results show that 14 of the 18 have very similar compositions: the iron mass fraction ranges about a factor of 3 around the solar value (assuming C/He = 3%) but abundance ratios X/Fe for elements from Na to Ba show little variation.
Journal ArticleDOI
Massive unseen companions to hot faint underluminous stars from SDSS (MUCHFUSS) - Analysis of seven close subdwarf B binaries
Stephan Geier,Pierre F. L. Maxted,Ralf Napiwotzki,R. H. Østensen,Ulrich Heber,H. Hirsch,Thomas Kupfer,Sebastian Müller,A. Tillich,Brad N. Barlow,R. Oreiro,R. Oreiro,T. A. Ottosen,Chris M. Copperwheat,Boris T. Gänsicke,T. R. Marsh +15 more
TL;DR: The Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) project as mentioned in this paper aims at finding hot subdwarf stars with massive compact companions like massive white dwarfs (M > 1.0 M� ), neutron stars or stellar mass black holes.
Journal ArticleDOI
Merger by migration at the final phase of common envelope evolution
TL;DR: In this article, it was shown that the CE α-prescription is insufficient to predict the final orbital separation of the CE evolution in massive envelopes in AGB and red super-giants stars with an envelope to secondary mass ratio of Menv/M2/m2−5.
Journal ArticleDOI
The 2D Distribution of Iron Rich Ejecta in the Remnant of SN 1885 in M31
TL;DR: In this article, the authors presented the HST ultraviolet Fe I and Fe II images of the Supernova 1885 (S And) which is observed in absorption against the bulge of the Andromeda galaxy, M31.
Journal ArticleDOI
The effects of variations in nuclear interactions on nucleosynthesis in thermonuclear supernovae
TL;DR: In this paper, the impact of nuclear physics uncertainties on nucleosynthesis in thermonuclear supernovae has not been fully explored using comprehensive and systematic studies with multiple models, and the authors investigate thermonnuclear reaction rates and weak interaction rates that significantly affect yields in their underlying models.
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