Townsley, D. M. and Gaensicke, B. T. (Boris T.) (2009) Cataclysmic variable primary effective temperatures : constraints on binary angular momentum loss. The Astrophysical Journal, Vol.693 (No.1). pp. 1007-1021. doi:10.1088/0004-637X/693/1/1007 ISSN 0004-637X.

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Abstract

We review the most decisive currently available measurements of the surface effective temperatures, T-eff, of white dwarf (WD) primaries in cataclysmic variables (CVs) during accretion quiescence, and use these as a diagnostic for their time-averaged accretion rate, <(M) over dot >. Using time-dependent calculations of the WD envelope, we investigate the sensitivity of the quiescent T-eff to long-term variations in the accretion rate. We find that the quiescent T-eff provides one of the best available tests of predictions for the angular momentum loss and resultant mass-transfer rates which govern the evolution of CVs. While gravitational radiation is completely sufficient to explain the <(M) over dot > of strongly magnetic CVs at all P-orb, faster angular momentum loss is required to explain the temperatures of dwarf nova primaries (nonmagnetic systems). This provides evidence that a normal stellar magnetic field structure near the secondary, providing for wind launching and attachment, is essential for the enhanced braking mechanism to work, directly supporting the well-known stellar wind braking hypothesis. The contrast in <(M) over dot > is most prominent for orbital periods P-orb > 3 h, above the so-called period gap, where <(M) over dot > differs by orders of magnitude, but a modest enhancement is also present at shorter P-orb. The averaging time which <(M) over dot > reflects depends on <(M) over dot > itself, being as much as 105 years for low-<(M) over dot > systems and as little as 10(3) years for high-<(M) over dot > systems. We discuss in some detail the security of conclusions drawn about the CV population in light of these time scales and our necessarily incomplete sample of systems, finding that, due to the time necessary for the quiescent T-eff to adjust, the consistency of measurements between different systems places significant constraints on possible long-timescale variation in (M) over dot. Measurements for nonmagnetic systems above the period gap fall below predictions from traditional stellar wind braking prescriptions, but above more recent predictions with somewhat weaker angular momentum loss. We also discuss the apparently high T-eff's found in the VY Scl stars, showing that these most likely indicate <(M) over dot > in this subclass even larger than predicted by stellar wind braking.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH):	Double stars, Stars, New, Cataclysmic variable stars, White dwarf stars, Dwarf novae
Journal or Publication Title:	The Astrophysical Journal
Publisher:	Institute of Physics Publishing, Inc.
ISSN:	0004-637X
Official Date:	1 March 2009
Dates:	Date Event 1 March 2009 Published
Volume:	Vol.693
Number:	No.1
Number of Pages:	15
Page Range:	pp. 1007-1021
DOI:	10.1088/0004-637X/693/1/1007
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	National Science Foundation (U.S.) (NSF), United States. National Aeronautics and Space Administration (NASA), Space Telescope Science Institute (U.S.) (STScI), Association of Universities for Research in Astronomy (AURA), United States. Dept. of Energy
Grant number:	PHY99-07949 (NSF), AST02-05956 (NSF), NAS5-26555 (NASA), PHY 02-16783 (NSF), DE-FG 02-91ER 40606 (DOE)

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