Rapid Variability as a Diagnostic of Accretion and Nuclear Burning in Symbiotic Stars and Supersoft X-ray Sources

Accretion disks and nuclear shell burning are present in some symbiotic stars (SS) and probably all supersoft X-ray binaries (SSXBs). Both the disk and burning shell may be involved in the production of dramatic outbursts and, in some cases, collimated jets. A strong magnetic field may also affect the accretion flow and activity in some systems. Rapid-variability studies can probe the interesting region close to the accreting white dwarf (WD) in both SS and SSXBs. I describe fast photometric observations of several individual systems in detail, and review the results of a photometric variability survey of 35 SS. These timing studies reveal the first clearly magnetic SS (Z And), and suggest that an accretion disk is involved in jet production in CH Cyg as well as in the outbursts of both CH Cyg and Z And. They also support the notion that the fundamental power source in most SS is nuclear burning on the surface of a WD, and raise questions about the structure of disks in the SSXBs. Finally, spectroscopic observations of RS Oph reveal minute-time-scale line-strength variations, probably due to a hot boundary layer. Taken together, the rapid timing observations explore the connections between jet-producing WDs and X-ray binaries, as well as SS, SSXBs, and CVs.