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Issue A&A
Volume 376, Number 2, September II 2001
Page(s) 448 - 459
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011004



A&A 376, 448-459 (2001)
DOI: 10.1051/0004-6361:20011004

Discovery of a cataclysmic variable with a sub-stellar companion

R. E. Mennickent1, M. Diaz2, W. Skidmore3 and C. Sterken4

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

(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 $13 000 < T_{\rm eff} < 24 000$ 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$\alpha$ 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 HeI 5875. As in other long cycle length dwarf novae, evidence for inner disk removal is found from the analysis of the emission lines.


Key words: accretion, accretion disks -- stars: binaries: close -- stars: individual: 1RXS J105010.3-140431 -- stars: novae, cataclysmic variables

Offprint request: R. E. Mennickent, rmennick@stars.cfm.udec.cl

SIMBAD Objects in preparation



© ESO 2001

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