Photometry Studies And Orbital Period Analysis Of W UMa Type Binaries YY Eri And LO And

Due to distinctive geometric structure of W UMa-type binary,there is a high probability of occultation,which is convenient for us to observe and obtain occultation data.In the past few decades,photoelectric metering and Charge Coupled Device?CCD?metering techniques have been increasingly advanced and widely used in observation and research,helping people to obtain a series of observation data and laying a foundation for the study of the structure and evolution of W UMa-type connected binary stars.1.we present new CCD photometric observations of the binary LO Andromedae in the BVR bands observed at the Xinglong station of the National Astronomical Observatories of China.Two new times of light minimum were derived from these observations.We modeled the light curve using the 2015 version of the 1971Wilson-Devinney program.The results show that the variations of the light curves can be explained if this star is a W UMa-type contact binary.The mass ratio was determined to be about 0.31.In addition,the orbital period variations of LO Andromedae were investigated using all of the photoelectric and CCD light minimum times,including our two new datasets.It was found that the period exhibits a possible period variation with a period of P_mod=26.44 years and a secular period increase of dP/dt=2.10×10^-7d?yr^-1.Since LO Andromedae is an overcontact solar-like system,we discuss three mechanisms for the mass transfer,responsible for the orbital period changes.2.Orbital period changes of the W UMa-type binary YY Eridani are analyzed by using all photoelectric and CCD times of light minimum.The results show that its orbital period is undergoing a secular increase superposed on two cyclic oscillations.The continuous increase at the rate ofdP/dt=.638×10^-8d?yr^-1may be accounted for by mass transfer.Two periodic variations with periods of P_mod=38.62 years and P_mod=22.36 years may be attributed to the light-time effect of a faint third star and the cyclic magnetic activity of the system respectively.