New Light Synthesis and Spectrum Synthesis Constraints on a Model for β Lyrae

Abstract

A suite of programs that calculates both synthetic light curves and synthetic spectra for a binary system with an optically thick accretion disk has been applied for the first time to β Lyrae A. Our results demonstrate that the standard accretion disk model by Hubeny & Plavec shows significant residuals from observations, both photometric and spectroscopic, and that no changes in adjustable parameters are able to remove the residuals. The basic problem is that the Hubeny & Plavec model requires a small visible segment of the hot star at the center of the accretion disk and this requirement conflicts with the photometric evidence. As an alternative, we investigate standard accretion disk models in which the central star is hidden from view. We find that no model of this type can satisfy either the observed photometry or the IUE spectra. To resolve this impasse, we suggest the presence of a light-scattering region above the accretion disk faces, which scatters light from the central star into the line of sight and provides the high-Teff radiation component required by both the light curves and the observed spectra. This source of radiation is very likely related to the jets proposed by Harmanec et al. and Hoffman et al. We calculate the location of stream impact on the accretion disk rim. Observations show no detectable photometric signature of a rim bright spot. We suggest that the liberated kinetic energy is spread over a region sufficiently large and at a sufficient optical depth to suppress appearance of a bright spot. A slight asymmetry of primary minimum may indicate swelling of the accretion disk rim downstream from the stream impact point, with an attendant slight increase in obscuration of the background light sources.