From Algol to Beta Lyrae

Abstract

We believe that we understand reasonably well the structure and evolutionary status of Algol and similar semi-detached systems, which will for brevity be called Algols. β Lyrae is much more complicated, and some of the problems of revealing its structure are discussed. The best model available at the present considers β Lyrae as an Algol-type semi-detached system in a phase of fairly rapid mass transfer, i.e. younger than typical Algols. The most important conclusion drawn in this article is that β Lyrae is not so unique as it is usually believed. Some characteristics that are so puzzling in β Lyrae actually appear already in such classical Algols like U Cephei and RW Tauri. The mass-accreting components in these systems are surrounded by a hot, turbulent layer which probably expands and which is the seat of emission lines of fairly high ionization discovered in the far ultraviolet. In β Lyrae and the so-called W Serpentis stars, the circumstellar hot turbulent shell is much more extensive and probably also denser, and may be forming a kind of a “superchromosphere”. Also, a trend appears among the W Serpent is stars for the gainers to be sorrounded by thick disks, and this trend, too, appears more forcefully in β Lyrae, where the disk propably completely sorrounds and hides the accreting star proper.