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| - Discovery of a cataclysmic variable with a sub-stellar companion
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| - We find that the ROSAT source 1RXS J105010.3-140431 is a cataclysmic variable with orbital period of 88.6 min and a spectrum closely resembling WZ Sge. In particular, emission lines are flanked by Stark-broadened absorption wings probably originating in the photosphere of a compact object. The Balmer absorption lines can be modeled by the spectrum of a DA white dwarf with $13 000 < T_{\rm eff} < 24 000$ K. The strong absorption lines allowed us to obtain direct radial velocities of the white dwarf using the cross-correlation technique. We find an extremely low white dwarf radial velocity half amplitude, $K_{\rm wd} = 4 \pm 1$ km s -1. This is consistent with the upper limit obtained from the H α emission line wing $K < 20$ km s -1. The corresponding mass function is incompatible with a main sequence secondary, but is compatible with a post orbital period minimum cataclysmic variable with a brown dwarf-like secondary. The formal solution gives a secondary mass of 10-20 Jovian masses. Doppler maps for the emission lines and the hypothesis of black-body emission indicate a steady state ( $T \sim r^{-3/4}$) accretion disk mainly emitting in H α and an optically thicker hotspot with a strong contribution to the higher order Balmer lines and He I 5875. As in other long cycle length dwarf novae, evidence for inner disk removal is found from the analysis of the emission lines.
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