Discovery of a cataclysmic variable with a sub-stellar companion

¹ Departamento de Fisica, Universidad de Concepcion, Casilla 160, Concepcion, Chile
² Instituto Astronomico e Geofisico, Universidade de Sao Paulo, Brazil
³ School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife, KY16 9SS, UK
⁴ University of Brussels (VUB), Pleinlaan 2, 1050 Brussels, Belgium

Corresponding author: R. E. Mennickent, rmennick@stars.cfm.udec.cl

Received: 15 January 2001
Accepted: 13 June 2001

Abstract

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 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, km s^-1. This is consistent with the upper limit obtained from the Hα emission line wing 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 () accretion disk mainly emitting in Hα and an optically thicker hotspot with a strong contribution to the higher order Balmer lines and HeI 5875. As in other long cycle length dwarf novae, evidence for inner disk removal is found from the analysis of the emission lines.