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arXiv · 0708.0097

SDSS J150722.30+523039.8: a CV formed directly from a detached white dwarf/brown dwarf binary?

S. P. Littlefair·V. S. Dhillon·T. R. Marsh·B. T. Gaensicke·I. Baraffe·C. A. Watson
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Abstract

We present high-speed, three-colour photometry of the eclipsing cataclysmic variable SDSS J150722.30+523039.8 (hereafter SDSS J1507). This system has an orbital period of 66.61 minutes, placing it below the observed ``period minimum'' for cataclysmic variables. We determine the system parameters via a parameterised model of the eclipse fitted to the observed lightcurve by chi^2 minimisation. We obtain a mass ratio of q = 0.0623 +/- 0.0007 and an orbital inclination i = 83.63 +/- 0.05 degrees. The primary mass is M_w = 0.90 +/- 0.01 M_sun. The secondary mass and radius are found to be M_r =0.056 +/- 0.001 M_sun and R_r = 0.096 +/- 0.001 R_sun respectively. We find a distance to the system of 160 +/- 10 pc. The secondary star in SDSS J1507 has a mass substantially below the hydrogen burning limit, making it the second confirmed sub-stellar donor in a cataclysmic variable. The very short orbital period of SDSS J1507 is readily explained if the secondary star is nuclearly evolved, or if SDSS J1507 formed directly from a detached white dwarf/brown dwarf binary. Given the lack of any visible contribution from the secondary star, the very low secondary mass and the low HeI(6678AA)/Halpha emission line ratio, we argue that SDSS J1507 probably formed directly from a detached white dwarf/brown dwarf binary. If confirmed, SDSS J1507 will be the first such system identified. The implications for binary star evolution, the brown-dwarf desert and the common envelope phase are discussed.

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S. P. Littlefair, V. S. Dhillon, T. R. Marsh, B. T. Gaensicke, I. Baraffe, C. A. Watson. 2007-08-01. SDSS J150722.30+523039.8: a CV formed directly from a detached white dwarf/brown dwarf binary?. https://doi.org/10.1111/j.1365-2966.2007.12285.x

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