Can a disk model explain Beta Lyrae?

Abstract

The Beta Lyrae eclipsing binary system is interpreted in terms of a model where the primary, i.e., spectroscopically observable, B star transfers matter to a 'canonical' accretion disk surrounding a 'gainer' which may be a rather ordinary B0.5 V star. Disk models are calculated using the TLUSDISK program. Most of the optical radiation from the secondary object is found to come from the disk rim, provided that the rate of mass transfer is not much lower than about 0.0001 solar mass per year. The rather high disk rim then introduces severe constraints on the orbital inclination; these constraints are discussed in detail. It is concluded that the disk plays an essentially passive role, and the observable radiation from its face is insignificant. A model in which most ultraviolet radiation would be coming from the face of the disk is found unacceptable both because of these constraints and because it would require an unrealistically small radius for the accreting star. It is proposed that the bulk of the ultraviolet radiation comes from a small unocculted segment of the gainer.