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Session 109 - Novae & Cataclysmic Variables.
Display session, Saturday, January 10
Exhibit Hall,

[109.10] A Search for Rapid Optical Variability in Symbiotic Binaries

J. L. Sokoloski, L. Bildsten (U. C. Berkeley), W. Ho (Cornell)

Symbiotic systems (SS) are wide binaries (P_orb \sim years) in which matter is accreted onto either a white dwarf (WD), main sequence star, or neutron star from a red giant. The accretion usually occurs via Bondi-Hoyle capture of the red giant wind, and the accreting hot component of the binary is surrounded by an emission line nebula. We present results from our ongoing search for rapid (minutes to hours) optical variability in symbiotic binaries using differential CCD photometry on the the 1-meter telescope at Lick Observatory. We are able to detect aperiodic variations of about 10 mmag in B and periodic variations of even smaller amplitude, and we have achieved time resolutions as high as 30 seconds. Dobrzycka et al. (1996, ApJ, 111, 414) performed a similar study of 8 symbiotics from 1992 to 1994 on the 1.2-meter telescope at Mt. Hopkins, and found flickering and possible quasi-periodic behavior in 3 objects. We have observed 7 of their objects as well as 14 others, nearly tripling the size of their sample. We have confirmed previous detections of aperiodic variability in 4 systems (MWC 560, CH Cyg, RS Oph, and T CrB), and have found evidence for flickering in at least one other. We compare these observations to the ubiquitous flickering seen in cataclysmic variables, which is generally attributed to an accretion disk. This comparison is interesting because it is not clear that all SS have stable disks, or which systems contain WD's. We also report our discovery of a persistent periodic signal at 28 minutes from one object. We are interpreting this periodicity as the spin period of a WD which has a field strong enough (>10^6 G) to funnel the accretion onto the dipolar caps.

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