ACCRETION DISK IN THE MASSIVE BINARY RY SCUTI

Abstract

The UBVR light curves of the massive eclipsing binary RY Sct, obtained at the Maidanak Observatory from 1979 to 1992, have been re-analyzed in order to prove the hypothesis of the presence of an accretion disk in the system. This hypothesis is supported by a new spectroscopic study of Grundstrom et al., and by a specific light-curve shape exhibiting a slight asymmetry around the secondary minima and a small difference in the height of the successive maxima. The light-curve analysis was performed using a Roche model of a binary containing a geometrically and optically thick accretion disk around the more massive primary star. By solving the inverse problem, the orbital elements and the physical parameters of the system components and of the accretion disk were estimated for all the individual UBVR light curves. The model gives a consistent solution for the RY Sct binary system and supports the hypothesis of the existence of an optically thick disk around the massive component. Our results suggest a mass exchange between the components and a mass loss from the system. This could be considered as a possible mechanism of the formation of the accretion disk around the more massive component and of the circumbinary envelope of toroidal form in the orbital plane of the system.