Journal Article

The shortest period detached white dwarf + main-sequence binary

S. G. Parsons, T. R. Marsh, B. T. Gänsicke, V. S. Dhillon, C. M. Copperwheat, S. P. Littlefair, S. Pyrzas, A. J. Drake, D. Koester, M. R. Schreiber and A. Rebassa-Mansergas

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 419, issue 1, pages 304-313
Published in print January 2012 | ISSN: 0035-8711
Published online December 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19691.x
The shortest period detached white dwarf + main-sequence binary

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We present high-speed ULTRACAM and SOFI photometry and X-shooter spectroscopy of the recently discovered 94-min orbital period eclipsing white dwarf/main-sequence binary SDSS J085746.18+034255.3 (CSS 03170) and use these observations to measure the system parameters. We detect a shallow secondary eclipse and hence are able to determine an orbital inclination of i = 855 ± 02. The white dwarf has a mass of 0.51 ± 0.05 M and a radius of 0.0247 ± 0.0008 R. With a temperature of 35 300 ± 400 K the white dwarf is highly overinflated if it has a carbon–oxygen core; however, if it has a helium core then its mass and radius are consistent with evolutionary models. Therefore, the white dwarf in SDSS J085746.18+034255.3 is most likely a helium core white dwarf with a mass close to the upper limit expected from evolution. The main-sequence star is an M8 dwarf with a mass of 0.09 ± 0.01 M and a radius of 0.110 ± 0.004 R placing it close to the hydrogen burning limit. The system emerged from a common envelope ∼20 million years ago and will reach a semidetached configuration in ∼400 million years, becoming a cataclysmic variable with a period of 66 min, below the period minimum.

Keywords: binaries: eclipsing; stars: fundamental parameters; stars: individual: CSS 03170; stars: low-mass; white dwarfs

Journal Article.  6369 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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