Photometric Investigations of Three Short-Period Binary Systems: GSC 0763-0572, RR Centauri, and ɛ Coronae Australis

CCD photometric observations of the short-period eclipsing binary GSC 0763-0572 were carried out in the B and V bands at Yunnan Observatory in China. Three light minimum times were determined from the observations and the orbital period of this system was revised. Photometric solutions for three W UMa-type stars (i.e., GSC 0763-0572, RR Cen, and ɛ CrA) were deduced by the 2003 version of the Wilson-Devinney code with and without third lights. All three systems are found to be A-type eclipsing binaries with low mass ratios. Combining with the radial-velocity curves for RR Cen (King, Hilditch 1984, MNRAS, 209, 645) and ɛ CrA (Goecking, Duerbeck 1993, A&A, 278, 463), the absolute parameters for those two binaries were redetermined. Based on all minimum times of RR Cen, it is found that the orbital period shows a long-term increase superimposed on a cyclic variation. The secular change with a rate of dP/dt = +1.21 × 10^-7 d yr^-1 may suggest that RR Cen is undergoing mass transfer from the secondary component to the primary one with dm/dt = +3.12 ×10^-8M_odot yr^-1. The cyclic oscillation with a period of 65.1(±0.4)yr and an amplitude of 0.0124(±0.0007) d may be explained by the presence of a third body, which can be identified by the revised photometric solution. It is believed that if the orbital period increases for those systems is true, this kind of binary may evolve into a rapid-rotating single star.