| In the first section of the present paper, the observational properties of W-type and A-type overcontact binaries are simply summarized. Some special overcontact binaries: (i )some overcontact binaries whose light curves exchange between W type and A type; (ii )some whose light curves are difficulty to classify as W type or A type; (iii) some whose light curves are A-type, but their physical parameters are similar to those of W-type systems; (iv)some whose light curves are A-type, but their photometric solutions indicate that the temperatures of the less massive components are higher than those of the more massive one, are introduced. Those observational properties all may suggest the shortage of Binnendijk's method. In the second section, based on the analyses of photometric observations, some new results of two overcontact binaries, Y Sex and RZ Com, are concluded as follows:1. CCD photometric observations of Y Sex in V band were obtained in March, 2003 and January, 2005 with the 1.0-m Cassegrain reflecting telescope at Yunnan Observatory. We found that the light curve of the system has changed obviously. Two new determined times of light minimum including the others collected from the literature were used to analyze the period change of Y Sex. Two periodic oscillations in the orbital period, one with a period of 60.2 years and an amplitude about 0.022 days and the other with a period of 30.1 years and an amplitude about 0.0060 days, were found. The two periodic changes may be caused by magnetic activity cycles in the two components or by light-time effects of additional bodies.2. Photoelectric observations in V band and CCD photometric data in B and V bands were obtained by using the 85-cm telescope at the Xinglong Station of NAO and the 1.0-m Cassegrain reflecting telescope at Yunnan Observatory. We found that the light curve of RZ Com have exchanged between W type and A type in the time interval from 1958 to 2004. And the presence of variable O'connell effect in the system was discovered. Compiling allavailable times of light minimum, we analyzed the period change of the system. A periodic oscillation with a period of 44.8 years and an amplitude of 0.0058 days was discovered to be superposed on the secular period increase(dP/dt = 44.12xlO"8days/years). The CCD light curves in B and V bands obtained in March, 2004 were analyzed by means of the Wilson-Devinney code. The mass ratio of the system q = 1/2.276 is similar to that of Mclean& Hilditch (1983) got from spectroscopic data. Our results showed that RZ Com is an overcontact binary system with the fillingdegree / = 21.6% .Combining the mass function derived by Mclean & Hilditch' (1983), we calculated out some physical parameters about RZ Com as following: Ml =1.14(±0.19) M ? , M2=0.5±0.09 M o ,R] =1.12±O.O1R0, R2 =0.78±0.01 RQ, and A = 2.41 ±0.02RQo... |
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