2000A&A...358..600T

We report the discovery of a new cataclysmic binary star from the ROSAT Galactic Plane Survey. The star has V>18.5 at minimum light and we have measured it as bright as V=15.7. Spectroscopy shows broad hydrogen and helium emission lines; HeII λ 4686 is not detected. Hα radial velocities yield an orbital period of 0.1429±0.0004d (3.430±0.010h). Time-series photometry covering one orbital cycle near maximum light shows irregular variability, but no evidence of an eclipse. The system appears to be a new dwarf nova of the U Gem or Z Cam type, and is unlikely to be a magnetic system. Its period is unusually short for a U Gem star. Curiously, the new cataclysmic binary is 83'' from the original ROSAT PSPC survey position, which puts it outside the PSPC positional uncertainty. Follow-up observations with the HRI reveal that the PSPC source is the superposition of two sources, and the cataclysmic is much the weaker of the two in X-rays. Its discovery in this survey is therefore essentially accidental. A V=19.4mag star is located 1.2'' from the stronger source's HRI position.