Accretion stream mapping of HU Aquarii

We present a new mapping algorithm, the Accretion Stream Mapping (ASM), whi ch uses the full phase-coverage of a light curve to derive spatially resolv ed intensity distributions along the accretion stream in magnetic cataclysm ic variables of AM Herculis type (polars). The surface of the accretion str eam is approximated as a 12-sided (duodecadon-shaped) tube. After successfu lly testing this method on artificial data we applied it to emission-line l ight curves of H beta, H gamma and He II lambda 4686 of the bright eclipsin g polar HU Aqr. We find hydrogen and helium line emission bright in the thr eading region of the stream where the stream couples on to magnetic field l ines. It is particularly interesting that the stream is bright on the irrad iated side facing the white dwarf, which highlights the interplay of collis ional and radiative excitation/ionization.