The Photometric Study And Orbital Period Investigation Of RT CrB?GSC 1537-1557 And AH Tauri

The close binary is an important type of binary star in the universe where more than 50% stars are binaries. They always show active and complex physical activities, such as chromospheric activity, Ca II H&K emission lines, starspot, orbital period change, etc. By observing the binaries and analyzing the light curve and O-C curve, we can obtain a lot of useful information to do research for the structure, evolution and interaction of the stellar.In this paper we first introduced the Wilson-Devinney method and the basic methods of investigating the orbital period. Then we modeled the light curves of RT Cr B, GSC 1537-1557 and AH Tauri using the Wilson-Devinney method, and analyzed the orbital period variation of those three close binaries. The main results are as follows:1. By using the Wilson-Devinney program we analyzed the light curve of the detached binary RT Cr B observed in 1985 and 2001 and obtained the photometric solution of RT Cr B and the parameter of the starspot. The wave-like distortions observed by Sabby and Lacy are most likely to be the effect of two starspots, a hot spot on the primary star and a cool spot on the secondary star. Through the studies of the orbital period a long-term period decrease at a rate of 7 1d P/ dt3.11 10 d yr--(28) ? have been found in the orbital period of RT Cr B which was possibly caused by the angular momentum loss via magnetic braking.2. With the analysis of the newly observed Rc and Ic data of the solar-type contact binary GSC 1537-1557, we have found that GSC 1537-1557 is a W-type contact binary with the mass ratio of q=M2/M1=2.645 and the degree of contact factor of f(28)(8.10 ±1.79)%. The photometric solutions suggest that the asymmetry and the distortion of the light curve may be caused by one hot spot on the primary component and one dark spot on the secondary component. In addition, our analysis of the O-C curve suggests that the orbital period of GSC 1537-1557 shows periodic oscillation with a period of 8.1 years and an amplitude of 0.00355 days which can be explained by the light-travel time effect caused by a third body which must be an extremely cool and dark stellar. The mass of the third body is estimated to be 0.19 M if the total mass of the system is adopted to be 1.31 M.3. We have derived two new times of light minima from the CCD photometric observations of AH Tauri observed in 2006 and obtained the photometric solutions through the analysis of the light curve using the Wilson-Devinney code. The type of the system was determined to be A-type; the fill-out factor and the mass ratio were computed to be 6.6% and 0.505, respectively. A cool spot on the primary star is the most suitable reason to explain the variations of the light curve. Combining our new times of light minima with all available data collected from the literatures we found a cyclic oscillation with a period of 54.62 years superimposed on a long-term period decrease at a rate of 71d P/ dt(1.823 0.215) 10 d yr--(28)- ± ?. The secular period change may be caused due to the mass transfer between the two components at a rate of 711 d M1.94 10 M yr--(28)- ? or the mass loss from the system via magnetic braking which the mass loss rate is 71d M/ dt4.97 10 M yr--(28)- ?. The plausible mechanism result in the cyclic oscillation is the light-travel time effect via the presence of a third body or the period magnetic activity on the active component.