Can a disk model explain beta lyrae?

The peculiar eclipsing binary system β Lyrae still eludes interpretation. We have attempted to interpret it in terms of a model where the primary, i.e., the spectroscopically observable B star transfers matter to a "canonical" accretion disk surrounding a "gainer" which may be a rather ordinary B0.5 V star. We calculated disk models using the program TLUSDISK, which computes the vertical structure of each disk ring self-consistently, without a priori assumption about its optical thickness, and then permits one to calculate the emergent radiation field at a number of frequencies and for various inclination angles. We find that most of the optical radiation from the secondary object probably comes from the disk rim, provided that the rate of mass transfer is not much lower than about 10^-4 solar masses per year. The rather high disk rim then introduces severe constraints on the orbital inclination; these constraints are discussed in detail. We conclude that the disk plays an essentially passive role, and the observable radiation from its face is insignificant. We find in particular that a model in which most ultraviolet radiation would be coming from the face of the disk is unacceptable both because of these constraints and because it would require an unrealistically small radius (≈ 1 R_⊙) for the accreting star whose mass exceeds 10 script M sign_⊙. We propose instead that the bulk of the ultraviolet radiation is coming from a small unocculted segment of the gainer, which probably is a rather normal main-sequence star of spectral type near B0.5 V, although a Wolf-Rayet star cannot be quite ruled out.