RAPID LIGHT VARIATIONS IN SYMBIOTIC BINARY STARS

We describe a search for short time scale light variations in eight sy mbiotic binary stars. Five systems-Z And, T CrB, AG Dra, BX Mon, and A X Per-do not vary significantly on minute time scales during any of ou r observations. Three other symbiotics-CH Cyg, RS Oph, and MWC 560-var y with amplitudes of Delta U greater than or equal to 0.2 mag and Delt a B approximate to 0.2-0.3 mag on time scales of minutes to tens of mi nutes. Our data confirm semicoherent variations with P approximate to 22 min in MWC 560. Similar variations with P approximate to 82 min are present in RS Oph. Our data are not extensive enough to test conclusi vely for periodic light changes in CH Cyg. Rapid photometric variation s in symbiotic stars have features in common with those observed in ca taclysmic binaries. In particular, three symbiotic stars with rapid pe riodic light variations have amplitudes and spin periods similar to th ose observed in the DQ Her subclass of cataclysmic binaries, These sys tems appear to follow the same spin period-B amplitude relation as the DQ Her stars, which suggests that some symbiotic stars contain magnet ic white dwarf secondaries. We also find a marginal correlation of fli ckering with luminosity; low luminosity hot components have a higher p robability of flickering than high luminosity systems. Confirmation of both correlations require larger sample sizes. (C) 1996 American Astr onomical Society.