PHASE-RESOLVED SPECTROSCOPY AND PHOTOMETRY OF THE ECLIPSING POLAR EP DRACONIS (=H1907+690)

We present phase-resolved optical spectroscopy and CCD photometry of t he faint eclipsing polar EP Dra (H1901+690). A revised ephemeris is de rived which connects all 32000 binary cycles since its discovery by Re millard et al. (1991). We found no difference between spin and and orb ital periods of the white dwarf. Changes in the light curve morphology are attributed to a different beaming behaviour which might change on timescales as short as one or several orbital periods. Optical light curve modelling was used to estimate the co-latitude of the accretion spot, which must be larger than 40 degrees. We have detected Zeeman ab sorption Lines of H alpha. originating in an accretion halo in a field of 16 MG. The low-resolution spectra reveal no indication of resolved cyclotron harmonics, which is also suggestive of a relatively low fie ld strength in the accretion region. The Balmer emission lines contain significant contributions from the UV-illuminated hemisphere of the c ompanion star, whereas the HeII lambda 4686 emission originates predom inantly from the accretion stream. The emission lines have a multi-com ponent structure and we could single out a narrow emission line in the H beta and H gamma lines. Its radial velocity amplitude suggests a lo w mass for the white dwarf, if the lines are interpreted as being of r eprocessed origin from the whole illuminated hemisphere of the compani on star.