The shortest period detached white dwarf + main-sequence binary

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

Monthly Notices of the Royal Astronomical Society, Volume 419, Issue 1, pp. 304-313.

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1
2012
Number of authors
11
IAC number of authors
0
Citations
42
Refereed citations
40
Description
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 = 85?5 ± 0?2. 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.
Type