The CV-like Short Timescale Light Variations Observed in Symbiotic Stars

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Session 61 -- Novae and Stellar Accretion
Oral presentation, Tuesday, 10, 1995, 10:00am - 11:30am

[61.06D] The CV-like Short Timescale Light Variations Observed in Symbiotic Stars

D. Dobrzycka (CfA)

The symbiotic stars (SS) form a relatively new and still poorly investigated class of interacting binary stars. Very little is known about the nature of their hot components. There are three types of possible models: disk accretion onto a main sequence star, disk accretion onto a white dwarf (WD), or a very hot stellar source. Rapid light variations were first observed in a few SS several decades ago (CH~Cyg, T~CrB and RS~Oph). Flickering is commonly observed in almost all cataclysmic variables and has come to be considered an observational proof of accretion onto a WD. By analogy, flickering in SS could also be interpreted in the same way, which would provide us with a confirmation of the model of a hot component as an accretion disk surrounding a WD. So far, there has been only one way of testing the hot component model (Kenyon \& Webbink, 1984, ApJ, 279, 252; M{\"u}rset et al. , 1991, A\&A, 248, 458). Unfortunately, it suffers from many difficulties, as it is based on the UV spectra not available for every SS and uncertainties due to interstellar reddening. Observations of the flickering have a chance to become a new method of determining the nature of the hot component.

I searched for short timescale light variations in a sample of ten SS representing a wide variety of hot components. I found flickering activity in RS Oph, CH Cyg and MWC~560 --- systems very likely containing a WD as a hot component. The MWC~560 light curve sometime shows periodic variations with a characteristic timescale of 23~minutes but other data reveal more random flickering. I did not find any obvious variations in the light curves of AX~Per, Z~And, BX~Mon, AG~Peg and T~CrB. The lack of flickering in T~CrB is very interesting, since this object has been known to flicker, e.g.\ in B, $\Delta m \sim 0.2$~mag (Bruch 1992, A\&A, 266, 237). I estimate the uncertainty of the observations of T~CrB in B at 0.02 mag; we should see flickering if there is any. This result may be important because the nature of the T~CrB's hot component is still unclear --- it could be either the WD or a main sequence star.

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