Starspot Cycles of RS Canum Venaticorum Type Stars

The starspot model was used to account for the photometric variations of RS Canum Venaticorum binaries. The twelve light curves of eight epochs for RS CVn, eleven light curves of six epochs for AR Lac and twelve light curves of nine epochs for V711 Tau were analyzed to investigate the cyclic variations of these systems. The spot parameters, as well as other elements of the systems, have been determined for each epoch by adjusting the parameters to fit the light curves. To avoid subjective parameter adjustment, the Wilson and Devinney differential correction computer program was adopted and modified for the adjustments of the spot parameters. Models were tested using one or two circular spots on the secondary stars. The adjustable parameters are latitudes, longitudes, radii, and temperatures of the spots, the surface potentials, albedos, temperatures of the two stars and the orbital inclination. The light curve fitting was done by adjusting the spot parameters and other parameters until a good fit to the entire light curve was obtained. We compared the one-spot model and the two-spot model for the three systems. A two spot-model adequately reproduces most light curves for the three systems. Of course, each model spot discussed here probably represents a spot grouping on the real star. To find the starspot cycles, only the spot longitude variations were considered. For RS CVn, starspot cycles of 9.22 years and 9.00 years were determined for two spots. These cycles agree with the 9.4 year cycle of the distortion -wave found by Catalano et al. For AR Lac, the cycles of the two spots are 11.26 years and 15.18 years, respectively. Finally 7.48 year and 7.09 year cycles were determined for V711 Tau.