Binaries of the Type W UMa

Abstract

High quality observations of complicated light curves have accumulated in recent years and efforts are being made to render large irradiation effects more tractable. The optical properties of the stellar atmosphere with respect to irradiation need be considered to arrive at a light-curve solution matching the observational precision. With this technical background, the short-period pairs of the W UMa type (cf. Figure 35 for comparison with other types) have commanded particular interest. The bona-fide identification with contact pairs, the possible models underlying the observed features, and the apparently isolated evolutionary status of this objects are interlocking problems, all related to the basic, unsolved question of their life span.