Littlefair, S. P., Dhillon, V. S., Marsh, T. R., Gaensicke, B. T. (Boris T.), Southworth, J. (John), Baraffe, I., Watson, C. A. and Copperwheat, C. M. (2008) On the evolutionary status of short-period cataclysmic variables. Monthly Notices of the Royal Astronomical Society, Vol.388 (No.4). pp. 1582-1594. doi:10.1111/j.1365-2966.2008.13539.x ISSN 0035-8711.

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Abstract

We present high-speed, three-colour photometry of seven short-period (P-orb <= 95 min) eclipsing cataclysmic variables (CVs) from the Sloan Digital Sky Survey. We determine the system parameters via a parametrized model of the eclipse fitted to the observed light curve by chi(2) minimization. Three out of seven of the systems possess brown dwarf donor stars and are believed to have evolved past the orbital period minimum. This is in line with the predictions that 40-70 per cent of CVs should have evolved past the orbital period minimum. Therefore, the main result of our study is that the missing population of post-period minimum CVs has finally been identified. The donor star masses and radii are, however, inconsistent with model predictions; the donor stars are approximately 10 per cent larger than expected across the mass range studied here. One explanation for the discrepancy is the enhanced angular momentum loss (e.g. from circumbinary discs); however, the mass-transfer rates, as deduced from white dwarf effective temperatures, are not consistent with enhanced angular momentum loss. We show that it is possible to explain the large donor radii without invoking enhanced angular momentum loss by a combination of geometrical deformation and the effects of starspots due to strong rotation and expected magnetic activity. Choosing unambiguously between these different solutions will require independent estimates of the mass-transfer rates in short-period CVs.

The white dwarfs in our sample show a strong tendency towards high masses. We show that this is unlikely to be due to selection effects. The dominance of high-mass white dwarfs in our sample implies that erosion of the white dwarf during nova outbursts must be negligible, or even that white dwarfs grow in mass through the nova cycle. Amongst our sample, there are no helium-core white dwarfs, despite predictions that 30-80 per cent of short-period CVs should contain helium-core white dwarfs. We are unable to rule out selection effects as the cause of this discrepancy.

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, Eclipsing binaries, Dwarf novae, Cataclysmic variable stars, Stars, New, Accretion (Astrophysics), White dwarf stars
Journal or Publication Title:	Monthly Notices of the Royal Astronomical Society
Publisher:	Wiley
ISSN:	0035-8711
Official Date:	21 August 2008
Dates:	Date Event 21 August 2008 Published
Volume:	Vol.388
Number:	No.4
Number of Pages:	13
Page Range:	pp. 1582-1594
DOI:	10.1111/j.1365-2966.2008.13539.x
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Version or Related Resource:	Littlefair, S. P., et al. (2008). On the evolutionary status of short period cataclysmic variables. AIP Conference Proceedings, 984, pp. 23-31.
Related URLs:	Related item in WRAP

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