Spectroscopy of the intermediate polars BG Canis Minoris and PQ Geminorum

BG CMi and PQ Gem both show an orbital cycle S-wave caused by the impact of the accretion stream with an accretion disc. In BG CMi the S-wave is occulted during a grazing eclipse, implying a relatively high inclination (~65 deg). The emission lines in both stars vary with the dominant X-ray pulses and at four orbital sidebands, including an omega-Omega pulse never seen before. These results, and other evidence, imply that the dominant pulsations occur at the white dwarf spin frequencies in both stars. They are thus disc-fed accretors. The Balmer lines in PQ Gem are incompatible with an origin in a disc or wind symmetric about the white dwarf, and their origin is unknown. The beat cycle pulse in both stars arises from reprocessing by the stream/disc impact region. Spin-pulse timings confirm that the white dwarf in PQ Gem is spinning down while that in BG CMi is spinning up. The emission lines in PQ Gem show complex changes over the spin cycle, arising in accretion curtains falling on to both magnetic poles of the white dwarf. I present the first Doppler tomography of these curtains. The implied phasing of the magnetic orientation is in excellent agreement with that recently proposed by Mason, including the fact that accretion occurs preferentially on to field lines leading the magnetic pole. This phasing is 180 deg different from that of BG CMi, and from that deduced by spectroscopy of other intermediate polars. The low velocities of the spin-cycle variations in PQ Gem suggest that it is at a low inclination (~30 deg).