THE ACCRETION HALO IN AM HERCULIS SYSTEMS

Previous phase-resolved spectropolarimetric observations of the AM Herculis systems V834 Centauri (E1405-451) and EF Eridani have shown broad, Zeeman-shifted absorption features during the bright phases. These features are thought to be non-photospheric in origin, and to arise from a cool 'halo' of unshocked gas surrounding the accretion shock on the surface of the white dwarf primary. We present preliminary models for the accretion halo region and use these models to perform a more detailed analysis of the relevant data for these two systems than has previously been done. We show that, in order to explain the observed halo Zeeman features, we require geometries which are consistent with the presence of linearly extended cyclotron emission regions. Such regions have previously been deduced from different considerations by other investigators. Our estimated masses for the accretion halo are comparable to the mass of the cyclotron emission region.