IRRADIATION OF THE SECONDARY STAR IN CATACLYSMIC VARIABLES

This paper shows how the relative strength of the Na I doublet over the surface of the secondary star can be calculated from radial velocity curves obtained using the Na I absorption feature around 8190 angstrom. The results for 11 dwarf novae and one magnetic cataclysmic binary system are presented. For the five dwarf nova secondary stars that showed significant heating, it is found that the surface distribution is far more asymmetrical than would be expected from irradiation by the white dwarf and disc hotspot. A possible mechanism for this asymmetry is circulation currents induced by the heating of the half of the secondary star's atmosphere facing the disc hotspot. There is also found to be an asymmetrical surface distribution for AM Her which cannot be explained using this argument, since there is no disc in this magnetic system.