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

Abstract

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, 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). Further observations revealed that the amplitude of this “flickering” increases with decreasing wavelength, which implied that it must be connected with the hot components. Flickering is commonly observed in almost all cataclysmic variables (CVs) and has come to be considered an observational proof of accretion onto a white dwarf. 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 white dwarf. So far, there has been only one way of testing the hot component model (Kenyon & Webbink, 1984, ApJ, 279, 252; Mürset 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.