DISCOVERY OF A NEW POLE-OCCULTING AM HER STAR USING THE ROSAT WIDE-FIELD CAMERA

We report the discovery of a probable new AM Her star, RE1149 + 28, in observations made with the ROSAT Wide-Field Camera. The light curve measured from the all-sky EUV survey data is highly variable and exhibits a 1-d periodicity which probably reflects an underlying binary period of either 90 or 103 min. The morphology of the modulation indicates that there is a single EUV-emitting pole in RE 1 149 + 28 and that this pole is rotated out of view, behind the white dwarf, for approximately half the binary orbital period. Optical spectroscopy shows clear evidence of systematic radial velocity motion in the emission lines at a period consistent with the 90- or 103-min photometric variation. The EUV data constrain the blackbody emission temperature to be between 10 and 40 Ev. RE1149 + 28 exhibits an unusually large EUV-to-optical flux ratio compared to previously known AM Her stars detected in the ROSAT survey.