The Orbital Period Investigation Of W UMa-type Contact Binaries

Because of their unique geometric configuration,the eclipse of W UMa-type contact binaries are easy to take place,which makes our observation possible.With the application of photoelectric and CCD photometric technologies in recent decades,A large amount of high precision observation data have been accumulated for this kind of binary system,which also makes us study the orbit period changes conditionally.In this paper,we select W UMa-type contact binary stars as the object of study.The orbit period changes of five samples(UY UMa,EF Boo,FG Hya,GR Vir and XY Boo)have been analyzed.The main results of period analysis are as follows:1.The study on the orbital period variations of UY UMa shows that this binary system has a long-term period increase at the rate of dP/dt = 2.55×10-7d yr-1,which may be due to the mass transfer from the secondary star to the primary star.Besides,UY UMa also shows a cyclic period change with a small amplitude of A = 0.0026 days and a period of Pmod=14.26 years superimposed on the secular period increase.This may be interpreted in terms of the light-time effect of the third body or magnetic activity of either star.2.The study of EF Boo shows that the orbital period of the system has a secular increase,and the rate is dP/dt= +2.62×10-7d yr-1,which may be due to the long-term mass transfer from the less massive component to the more massive one and the transfer rate is dM2/dt =-3.35×10-7M? yr-1.3.By careful study of FG Hya,we find that the orbit period of FG Hya shows a non-sinusoidal periodic variation,which may be due to a third body in an eccentric orbit.Moreover,it is obtained that the modulation period of the orbit is Pmod = 54.44 years,the minimum mass of the third body is 2.14M?,and that this maybe an unseen star.4.In the analysis of the orbital periodic variation of GR Vir,we have found an oscillation with an amplitude of A = 0.0352 days and a period of = 28.56 years.This periodic oscillation may be due to the light-time effect of the additional companion or magnetic activity of either star.5.There are two period variation components in XY Boo:a periodic change is superimposed on the long-term increase.The increase rate is calculated to be dP/dt = 2.04×10-7d yr-1,which may be caused by the mass transfer from the less massive star to the more massive star.The non-sinusoidal periodic oscillation component may be due to the light-time effect of a third body in an eccentric orbit.