EUVE J0425.6-5714: A newly discovered AM Herculis star

We detected a new AM Her star serendipitously in a 25 day observation with the EUVE satellite. A coherent period of 85.82 minutes is present in the EU VE Deep Survey imager light curve of this source. A spectroscopic optical i dentification is made with a 19th magnitude blue star that has H and He emi ssion lines, and broad cyclotron humps typical of a magnetic cataclysmic va riable. A lower limit to the polar magnetic field of 50 MG is estimated fro m the spacing of the cyclotron harmonics, EUVE J0425.6-5714 is also detecte d in archival ROSAT HRI observations spanning 2 months, and its stable and highly structured light curve permits us to fit a coherent ephemeris linkin g the ROSAT and EUVE data over a 1.3 yr gap. The derived period is 85.82107 +/- 0.00020 minutes, and the ephemeris should be accurate to 0.1 cycles un til the year 2005, A narrow but partial X-ray eclipse suggests that this ob ject belongs to the group of AM Her stars whose viewing geometry is such th at the accretion stream periodically occults the soft X-ray emitting accret ion spot on the surface of the white dwarf. A nondetection of hard X-rays f rom ASCA observations that are contemporaneous with the ROSAT HRI shows tha t the soft X-rays must dominate by at least an order of magnitude, which is consistent with a known trend among AM Her stars with large magnetic field s. This object should not be confused with the Seyfert galaxy 1H 0419-577 ( =LB 1727), another X-ray/EUV source that lies only 3.'95 away and that was the principal target of these monitoring observations.