General properties of W Ursae Majoris systems

The authors have assembled a sample of 42 W Ursae Majoris binary systems (21 W-type, 21 A-type) whose light curves have all been solved by means of the Wilson & Devinney method. The masses, radii and luminosities have been derived assuming the global physical properties of a system are the same as for an analogous detached one, and therefore without any constraint on the physical parameters of the primary star. The main results of this procedure are: (i) the discovery of a substantial continuity of the physical properties from W-type to A-type, suggesting a scenario in which almost all A-type systems are the evolved counterparts of W-types; (ii) the existence of an inhomogeneous group probably evolved into contact from a detached configuration. This second group has no evolutionary link with the RS CVn-like systems, which seemed at first to be suitable candidates as parent stars. An upper limit for the primary mass of unevolved objects is derived.