The stream impact region in the disc of WZ Sge

We report the observation of new features in the spectrum of the cataclysmic variable WZ Sge. The disc eclipse is seen as a well-defined structure in the H alpha, line. From phases 0.25 to 0.5 an absorption feature of the same shape as the emission S wave is seen in this line, but redshifted by similar to 200 km s(-1). Two possible interpretations of this feature are given, both of which imply that it originates at the impact point of the stream on the disc edge. In addition, evidence is found for substructure in the velocity map of the spot. Emission from line-emitting post-shock material, extending to about 60 degrees downstream from the continuum hotspot, is seen in the Doppler map in the form of a tail extending from the hotspot. A theoretical estimate shows that such a tail is to be expected as a consequence of the post-impact hydrodynamics of the stream. A new determination of the system parameters is made. They agree with those of Gilliland et al.; in particular, the data support a high primary mass. The variation of H alpha surface brightness with distance from the primary is flatter, in the inner regions, than the r(-1.5) dependence found by Horne for other cataclysmic variables in quiescence.