HST studies of cataclysmic variable white dwarfs

Abstract

HST spectroscopy of faint exposed white dwarfs (WDs) in cataclysmic variables (CVs) has provided fundamental new information on white dwarf rotation rates, T eff, log g, chemical abundances of their accreted atmospheres, cooling response to heating of the white dwarf by boundary layer irradiation, compression and shear mixing in consequence of dwarf nova outburst events, and determined WD masses independent of disk emission line velocities. The first spectroscopic evidence of an accretion belt, predicted by Kippenhahn and Thomas, was uncovered in VW Hydri. The abundances and mix of nuclei in two white dwarfs in dwarf nova systems show signs of thermonuclear events in the recent past. In one of the cases, contamination of the secondary during a common envelope stage and re-accretion by the white dwarf, of its processed material, may be indicated. Although the detailed studies are few in number thus far, we have many promising indications of breakthroughs I would like to report at this conference. My focus will be on the essentially non-magnetic or weakly magnetic, tangentially accreting systems.