We find that the ROSAT source 1RXS J105010.3-140431 is a cataclysmic variable with orbital period of 88.6 minutes 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 _ { 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 _ { wd } = 4 \pm 1 km s ^ { -1 } .
This is consistent with the upper limit obtained from the H \alpha 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 \alpha 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 .