Abstract
The authors describe simultaneous ultaviolet and optical, as well as other observations of MR Ser during a high state. No substantial linear polarization was observed during an orbital cycle, but the circular polarization was high. The ultraviolet spectrum presents strong lines in emission of N V λ1240, Si IV λ1400, C IV λ1550 and He II λ1640, typical of other AM Her systems, and also shows semi-forbidden lines of N IV] λ1486, O III] λ1663 and N III] λ1750, not detected previously in similar objects. An analysis of the physical conditions in which these lines are produced is presented. The authors compare the optical emission with that expected from cyclotron emission in AM Her objects. The orbital ephemerides are revised, and an improved period of 0.0788698±0.000005 days is found.
