Time resolved circular polarimetry of white dwarf pulsars

There are two recognized subsets of cataclysmic binaries that contain white dwarfs: the AM Her stars, whose white dwarf components are sufficiently magnetized to ensure synchronous rotation with the orbital period, and the DQ Her stars, which do not maintain synchronism and probably have been spun up by mass accretion. A pilot survey has shown that for all objects but V533 Her the amplitude of the periodic component of the circular polarization is not greater than 0.10-0.15% in the blue band. In the case of V533 Her approximate 0.5% sinusoidal changes in a circular polarization have been detected on two nights. This might mean that in DQ Her stars the dilution by an unpolarized background is very large, and furthermore, that this dilution is variable. (Auth.)