Accretion Stream Mapping of HU Aquarii

Abstract

We present a new mapping algorithm, the "Accretion Stream Mapping (ASM)" which uses the full phase-coverage of a light curve to derive spatially resolved intensity distributions along the accretion stream in magnetic cataclysmic variables of AM Herculis type (polars). The surface of the accretion stream is approximated as a duodecadon shaped tube. After successfully testing this method on artificial data we applied it to emission line light curves of Hbeta, Hgamma and He II lambda 4686 of the bright eclipsing polar HU Aqr. We find Hydrogen and Helium line emission bright in the threading region of the stream where the stream couples onto magnetic field lines. It is particularly interesting, that the stream is bright on the irradiated side, facing the white dwarf, which highlights the interplay of collisional and radiative excitation/ionization.