STROMGREN U PHOTOMETRY OF CH CYGNI IN 1995 AND 1996

Rapid time resolution, Stromgren u-band photometry of CH Cygni shows a marked decrease in quasi-periodic, short-time-scale (similar to 2000- 3000 s) variability between 1995 August and 1996 June. In 1995, we det ected variability of similar to 0.3-0.4 mag with periods of approximat e to 2200 s and approximate to 2700 s, which are remarkably similar to periods reported by Hoard (1993) from similar u-band measurements of CH Cyg in 1992. In contrast, during a number of nights in 1996 the u m agnitude was roughly constant within 0.1 mag, and the light curves sho wed no evidence of rapid variability. The average u magnitude of CH Cy g decreased by similar to 0.9 mag between 1995 and 1996, suggesting a common source for the quasi-periodic variability and the u-band lumino sity, namely the hot component in the interacting binary. We discuss s everal possible explanations for this variability, including the spin of an accreting, magnetic white dwarf (as in the intermediate-polar cl ass of cataclysmic variables) and the reprocessing of accretion-induce d radiation from the white dwarf in circumstellar material.