Published online by Cambridge University Press: 12 April 2016
There has been considerable interest recently in the AM Herculis binaries, which are believed to contain a strongly magnetic white dwarf accreting matter from a lower-main-sequence companion (Tapia 1977, Chanmugam and Wagner 1977, Stockman et al. 1977). Models for these systems feature an accretion column above a magnetic pole of the white dwarf. A shock-heated region, with a temperature kT ≈ 20 keV (Raymond et al. 1979) and a height h – 106cm (Masters 1978), believed to be formed in AM Her just above the magnetic pole is likely to be responsible for the emission of the hard X-rays observed (Swank et al. 1977). It has been further suggested that this region should emit optically thick cyclotron emission in the ultraviolet because of the presence of the strong magnetic field ~ 108 gauss (Masters 1978, Lamb and Masters 1979). Such UV emission has not been observed (Raymond et al. 1979).