THE DISCOVERY OF RE-1307- THE SHORTEST PERIOD AM-HER-SYSTEM(535 )

We report on a ROSAT Wide Field Camera EUV survey observation of RE 13 07 + 535 which, together with optical spectroscopic and photometric ob servations, shows that this object is an AM Her system. These observat ions reveal that RE 1307 + 535 has an orbital period of 79.69 min, the shortest orbital period known for such a system. RE 1307 + 535 was ob served by us in both high (V = 17-18) and low (V = 20-21) states, with evidence of cyclotron emission being seen in both cases. We use the h igh-state spectroscopy to show that the optical emission comes from a region with a magnetic field, B approximate to 30-40 MG. We derive EUV temperature and luminosity limits. IRCAM infrared photometry is used to put a lower limit on the distance to RE 1307 + 535 of d > 705 pc. R E 1307 + 535 is thus one of the most distant AM Her systems known, and is the first that is at a measured distance of z > 630 pc above the G alactic plane.