Observation And Study On Over Contact Binaries In The Galactic Clusters

The overcontact binary in star clusters is a system whose components both fill their Roche lobe and there is a convective common envelope. It is more predominant than the field star in researching. In this paper, overcontact binaries in open clusters were observed, analyzed and studied. Meanwhile, the observational and theoretical studies for star clusters and overcontact binary are also summarized briefly, the results are obtained as follows:1. It was found that the number of the overcontact binary in open cluster is in line with the age of cluster. That means the old one has more overcontact binaries. It supports the viewpoint of overcontact binaries was a stage of binaries.2. The distribution of amplifications about the overcontact binaries were studied. We found that the relationship between the number of the detected overcontact binaries and the orbital inclination more likely is dNαsin²idi according to the computer's simulation. It fit very well under this condition. Moreover, the efficient radiation area ratio R_s was defined, which maybe become a consulted parameter to estimate whether there is an additional body in the system.3. overcontact binary BH Cen and V701 Sco in the extremely young open cluster IC2944 and NGC6383 were analyzed, we found that the period of BH Cen was increasing with a rate +1.70(±0.39)×10^-7day/year. And meanwhile, a period of the orbital period oscillation was determined to be P₃=44.6year,A₃=0.0216day. But there was not long-term changes in V701 Sco whose mass ratio is unit except a period oscillation as P₃=41.1year,A₃=0.0112day. All of those period oscillations show that the two system both possess a third body. It is thought that the center system develop a overcontact stage in a short life time via the third body remove angular momentum. Meanwhile, it clarify that it is short of faint stars in young clusters because of the invisible third body associated with the bright OB stars.4. We used the PI1024 TKB CCD photometric system attached to the 1.0-m reflecting telescope at the Yunnan Observatory to observe the overcontact binary TX Cnc which is a member of the young cluster M44 for five nights (December 30, 2003; March 16 and December 18, 19, 2004; March 29, 2006). The observations obtained on December 18 & 19, 2004 are complete in the V band. Through using the W-D code, we found that it is a medium mass ratio and shallow contact system with the overcontact factor 24.8%. And its orbital period is long-term increase with a rate+5.61×10^-8day/year. A cyclic oscillation with an amplitude of A₃=0.0026days was discovered to be superposed on a continuous period increase. This may reveal that there is a third body in the system. We derived its basic parameters:M₁=1.319±0.007M_☉, M₂=0.600±0.01M_☉; R₁=1.28±0.19R_☉, R₂=0.91±0.13R_☉.5. We used the PI1024 TKB CCD photometric system attached to the 1.0-m reflecting telescope at the Yunnan Observatory to observe the overcontact binary AH Cnc which is a member of the old cluster M67 for several years (from Jan, 2001 to Apt, 2005). Many data was obtained. The observations obtained on 2001 are complete in the B V band and on 2002 are complete in the V band. Comparing the data of the two difference years, it shows changes exist between phase 0.15 and 0.56. Through using the W-D code, we found that it is a low mass ratio and deep contact system with the overcontact factor 58.5%. And its orbital period is long-term increase with a rate +3.99(±0.14)×10^-7day/year. Two cyclic oscillations with the period of P₃=36.5year and P₄=7.75year and was discovered to be superposed on a continuous period increase. We got its basic parameters are as follows: M1=1.10±0.09M_☉, M₂=0.19±0.02M☉.