1994A&A...291L..27R

We report the discovery of a new AM Herculis system (polar) identified as the optical counterpart of the bright, soft, high-galactic latitude X-ray source RX J0531.5-4624 detected during the ROSAT All-Sky Survey. Optical spectroscopy of the V~=17mag object shows systematic radial velocity variations of the emission lines with an orbital period of 133.5min, placing the object well within the period gap of cataclysmic variables. The X-ray flux is ∼80% modulated with the same period and has two maxima per orbital cycle. Optically, the system varies by ∼1mag around the orbit. The morphology of the light curve has, however, changed significantly within a few months. From cyclotron harmonics seen in the red wavelength range of a low-resolution spectrum, we derive a magnetic field strength in the accretion region of B∼19MG. The relative intensity of the spectral features of the secondary star implies a distance of d∼300pc.