Observations Of W UMa-type Contact Binaries

W Ursae Majoris contact binaries are very common variables, a density of1/500main-sequence stars in the solar neighborhood was estimated by Rucinski.The components of W UMa contact binaries have flled their inner Roche lobe andshare a common envelope, so there are complicated physical processes in contactbinaries. The study of W UMa contact binaries have important meaning inenriching the evolution theory of binaries and studying the formation of peculiarstars. In this thesis, we summarize the observational characteristics of W UMacontact binary. The physical processes and evolution status of W UMa contactbinaries are also discussed. Besides, we give the photometric study of a W UMacontact binary HH UMa.New BV light curves of HH UMa were obtained with1m Cassegrain refectortelescope at Yunnan Observatories. The B and V light curves of HH UMa andradial velocity published by the previous investigators are analyzed by using the2003version of the Wilson-Divinney (W-D) code. Then we obtain a simultane-ously solution and absolute parameters for HH UMa. We fnd that HH UMa isa W-type W UMa system with a mass ratio of q=m2/m1=3.344and a con-tact degree of f=31.9%. The temperature diference between two componentsis247K. The asymmetry of the light curves can be explained by adding a hotspot located near the neck region of the more massive component. We conduct aperiod investigation based on O-C diagram. By using the absolute parameters,we estimate the mass transfer rate between two components. Then we discussthe evolution status of HH UMa, and we fnd the system has not evolved awayfrom ZAMS stars.