The Observation And Investigation On The O’Connell Effect Of Late-type Contact Binaries

Late-type contact binaries refer to contact binaries with two components whose spectral types are F,G,K or M types,which generally exhibit strong magnetic activity,similar to sunspots or solar flares and so on.Thus,the asymmetry at maximum light is observed from the light curves,namely,the O’Connell effect,or emission lines from the spectra that exhibit chromospheric activity.Therefore,we analyzed the long-time or short-time scale light curves and the characteristics of spectral emission lines of some special latetype contact binaries through long-term observations and studies,and then proposed new theories and hypotheses on their structure and evolution,which provided new directions and guidelines for the future study of O’Connell effect.In this thesis,we first introduce the background,current status and significance of the contact binary research,then list the observation equipment we used,and the tools and methods used in the analysis process.In the following part,we analyze and discuss a total of nine late-type contact binaries,explore the pattern between the O’Connell effect exhibited by the late-type contact binaries and the spectral emission lines and magnetic activity of the cool spot.The last part is the conclusions and prospects.The research results are divided into the following three parts:1.Using W-D code,the analysis of five neglected W UMa contact binaris of EF CVn,EH CVn,FP Lyn,FV CVn and V345 UMa was performed through the multi-passband light curves.We obtained that EF CVn is a median contact binary,while EH CVn,FP Lyn,FV CVn and V345 UMa are all shallow contact binaries,and they are all W-type contact binaries.For the asymmetric light curves of EF CVn,FP Lyn and V345 UMa,we used the cool spot or hot spot models to fit.The analysis of orbital period shows that all five targets have long-term increasing or decreasing components,which may be caused by mass transfer or angular momentum loss.Meanwhile,the O-C curves of EF CVn and FV CVn also show periodical changing,which is most likely explained by the light time travel effect(LTTE)caused by the third body.2.For ASAS J124343+1531.7,LINEAR 2323566 and NSVS 2536063,the light curves and LAMOST spectra were analyzed,and the absolute physical parameters were determined by W-D code.The mass ratio and contact degree were determined as 3.758,1.438,0.308 and 32%,15%,26%,respectively.They all exhibit O’Connell effect,which can be perfectly explained by using the cool spot or hot spot model during W-D fitting.Furthermore,we measured the equivalent widths(EWs)of their Ha line by the spectral subtraction technique,and the emission lines of Ha indicate that they may all show magnetic activity.And it shows that the larger EW of Hα line,the more obvious O’Connell effect.Both ASAS J124343+1531.7 and NSVS 2536063 may have long-term increases in their orbital periods,which probably due to the mass transfer from the more massive star to the less massive star.3.Combined with the multi-passband light curves in ten years and one set of radial velocity curve,we determined the physical parameters of NR Cam.NR Cam is a Wtype shallow contact binary.The long timescale light curves of NR Cam exhibit obvious O’Connell effect-We fitted 21 sets of light curves by adding a cool spot on the primary star and a cool spot on the secondary star,respectively,and obtained the spot parameters and geometric structure changes of NR Cam in different years.There may be a 6.7 yr magnetic cycle,as suggested from the analysis of Δm(Max.Ⅱ-max.Ⅰ)and O’Connell effect ratio(OER)for the long time scale data.The O-C analysis of NR Cam for about 12 yr demonstrates that its period is experiencing a long-term decrease accompanied a cyclic oscillation component with a period of 9.17 yr.The cyclic oscillation might be caused by the LTTE due to a third body.The corresponding trends of O-C values,longitude and angular radius of spot.Am,and OER for the high precision TESS data confirm that NR Cam exhibits strong magnetic activity and that the changes of spots in the short time scale affect the changes of O-C values.Investigations of the orbital angular momentum Jorb and progenitors suggest that NR Cam may be a newly formed young contact binary,and considering the small contact degree,may be exhibiting thermal relaxation oscillation(TRO).In summary,nine contact binaries were studied in this thesis.Except for NR Cam,all the other eight contact binaries were analyzed for the first time by photometric solutions and orbital period analyses,and the EWs of the LAMOST spectral Hα lines of three targets were analyzed by the spectral subtraction technique.The analysis of NR Cam also used the radial velocity curve.Finally,we determined the absolute physical parameters of these nine targets and obtained new ephemerides and the law of orbital period changes.It is confirmed that the larger EWs of Hα lines,the more obvious O’Connell effect of the light curves will be.There may be a solar-like magnetic activity cycle in NR Cam,and there may be weakly correlated between its Am and O-C and the spot parameters,confirming the variation of spot parameters will affect the variation of O-C.The results of this paper provide observational evidence for explaining the O’Connell effect with the magnetic spot model,and promote the understanding of the relationship between the spot parameters and the variations of O-C,and provide observational evidence for enriching and perfecting the theoretical model of contact binaries.