Binary systems at and beyond the short-period limit of WUMa systems

Abstract

The short-period limit of W UMa-type contact binaries of about 0.22 days is very sharp and well de ned. Observations and investigations of close binaries beyond this limit can provide important information on the origin and evolu- tionary processes of contact binaries, as well as on the formation and migration history of low-mass stars. In the past several years, we have monitored some close binaries below the short-period limit by using several small telescopes and 2m-class telescopes. Photometric solutions and period changes of these binary stars were analyzed and investigated. Some new contact binaries below the limit were detected. Our results reveal that the rarity of contact binaries below the short-period limit could not be explained by rapid dynamical destruction.