The secondary component of beta Lyr.

Abstract

Quantitative analysis of fl Lyr light curves shows that thin-disk and "no-disk" models for the secondary can be ruled out, leaving (presumably) only a thick-disk model. Some common assertions about the asymmetry and repetition of the light curves are not supported by examination of the existing observations. There is no evidence that the secondary component is underluminous for its mass, provided the observations are interpreted in terms of a thick secondary disk, most of whose luminosity emerges at the poles. The polar effective temperature of the disk is several thousand degrees K higher than that of the primary component, and is therefore the obvious candidate for the elusive source of excitation for the B2-B5 shell spectrum. Because the secondary is not underluminous, there is, at present, no reason to postulate the presence of a collapsed star at its center. Reasons are given to explain why the secondary spectrum has not been seen, despite the fact that the observed continuum flux from the secondary is of the order of one-half that from the primary. Estimates of this flux in previous work were much lower. The mass ratio, 2/ 1, is estimated to be 4.2 (+3.0, - 1.8) if the chemical abundances found by Boyarchuk are adopted, or about 6, with similar uncertainty, if abundances by Hack and Job are used. It is argued that the disk must be in strongly differential rotation. Future work on modeling the system might well assume the basic semitoroidal geometry of the Bodenheimer-Ostriker differentially rotating model stars. Most of the secondary mass probably lies in an embedded main-sequence star, rather than in the disk, which is probably of the order of one, or perhaps a few, solar masses. Subject headings: eclipsing binaries - stars, individual