Photometric And Statistical Studies Of W UMa-type Contact Binaries

W UMa-type contact binaries are the most widely observed and studied type of eclipsing binaries.They are a natural laboratory to study the inner structure and physical processes occurring between two their components,and a good support to detect the third bodies orbiting them.Furthermore,photometric,orbital period variations and statistical studies of W UMa-type contact binaries are,in theory,significantly valuable for understanding the formation,evolution and final destination of contact binaries.In this thesis,the first photometric studies and orbital period variation investigations for four W UMa-type contact binaries have been performed.Also,based on 183 samples of contact binaries,we performed a statistical investigation of their orbital and physical parameters.The main contents and conclusions of this thesis are presented as follows.(1)Four W UMa-type contact binaries: V473 And,V805 And,LQ Com,and EG CVn,have been observed using the 60 cm and 85 cm telescopes at Xinglong Station of National Astronomical Observatories of China,respectively.Their full BVR-bands light curves have been obtained and the slight asymmetries,i.e.,the weak O’Connell effects,are found in the light curves of V805 And and EG CVn.Their light curves have been analyzed by using the Wilson-Devinney code.The photometric solutions suggested that V473 And and LQ Com are two A-subtype contact binaries,while V805 And and EG CVn belong to W subtype.The weak asymmetries in the light curves of V805 And and EG CVn may be interpreted as a result of a cool spot on the primary,respectively.Combining our photometric solutions with two different method(the schemes based on Gaia distance and empirical relation),both orbital and physical parameters for four targets were well determined.(2)Based on all available eclipse timings,we systemically investigated the orbital period variations and the corresponding physical origins for the four samples.The results show that the orbital period of LQ Com is stable for the last two decades,while the remaining three targets exhibit a cyclic period variation.Additionally,the orbital periods of V805 And and EG CVn are accompanied by a secular decrease and increase,respectively.The secular period variations are caused mainly by the mass transfer between two components,while the cyclic period oscillations may be interpreted as the results of either the light-time effect due to the third body or the cyclic magnetic activity.(3)We made a statistical investigation of orbital and physical parameters for 183 contact binaries with reliable physical parameters,and confirmed some statistical correlations between orbital and physical parameters.Also,some statistical differences between A-and W-subtype contact binaries were uncovered.The statistical results suggested that the A-subtype contact binaries have,in general,longer orbital periods and semi-major axises,more total masses and orbital angular momenta,larger temperature differences between two components,than the W-subtype ones.These imply that the A-subtype systems are younger than the W-subtype ones.Furthermore,the A-subtype systems may evolve into W-subtype systems via the mass and angular momentum loss,but the opposite evolutionary direction seems to be unlikely.