Marsh, T. R., Gänsicke, B. T. (Boris T.), Steeghs, D. (Danny), 1972-, Southworth, J. (John), Koester, Detlev, 1941-, Harris, V. and Merry, L.. (2011) Detection of a white dwarf companion to the white dwarf SDSSJ125733.63+542850.5. The Astrophysical Journal, Vol.736 (No.2). p. 95. ISSN 0004-637X

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Abstract

SDSSJ125733.63+542850.5 (hereafter SDSSJ1257+5428) is a compact white dwarf binary from the Sloan Digital Sky Survey that exhibits high-amplitude radial velocity variations on a period of 4.56 hr. While an initial analysis suggested the presence of a neutron star or black hole binary companion, a follow-up study concluded that the spectrum was better understood as a combination of two white dwarfs. Here we present optical spectroscopy and ultraviolet fluxes which directly reveal the presence of the second white dwarf in the system. SDSSJ1257+5428's spectrum is a composite, dominated by the narrow-lined spectrum from a cool, low-gravity white dwarf (T eff 6300 K, log g = 5-6.6) with broad wings from a hotter, high-mass white dwarf companion (11, 000-14, 000 K; ~1 M ). The high-mass white dwarf has unusual line profiles which lack the narrow central core to Hα that is usually seen in white dwarfs. This is consistent with rapid rotation with vsin i = 500-1750 km s–1, although other broadening mechanisms such as magnetic fields, pulsations, or a helium-rich atmosphere could also be contributory factors. The cool component is a puzzle since no evolutionary model matches its combination of low gravity and temperature. Within the constraints set by our data, SDSSJ1257+5428 could have a total mass greater than the Chandrasekhar limit and thus be a potential Type Ia supernova progenitor. However, SDSSJ1257+5428's unusually low-mass ratio q 0.2 suggests that it is more likely that it will evolve into an accreting double white dwarf (AM CVn star).

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Double stars, Supernovae, White dwarf stars
Journal or Publication Title:	The Astrophysical Journal
Publisher:	Institute of Physics Publishing, Inc.
ISSN:	0004-637X
Date:	August 2011
Volume:	Vol.736
Number:	No.2
Page Range:	p. 95
Identification Number:	10.1088/0004-637X/736/2/95
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	Science and Technology Facilities Council (Great Britain) (STFC)
Related URLs:	Other Repository
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URI:	http://wrap.warwick.ac.uk/id/eprint/38572

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