Photometric study of the short-period RS Canum Venaticorum binary RT Andromedae

Abstract

Context. Long-term photometric observations of cool stars can reveal the evolution and activity cycles of the stellar active region. Furthermore, studying the stellar activity provides opportunities for understanding of stellar dynamo and valuable constraints for stellar dynamo theory. Aims. We analyze our observational data and discuss light-curve variability due to starspots on both a short and long time scale, especially the short-term variation. At the same time, we accumulate some results from the literature to discuss active-region evolution and activity cycles. Methods. By analyzing the light curves using the Wilson-Devinney program, the photometric solution of the system is obtained and the starspot parameters are also derived. Using the phase-dispersion minimization method, we infer the activity cycle of RT And. Results. The case of two spots being on the primary is most successful in reproducing the light curve distortion of RT And in 2004. Although the light curves in 1999 and 2005 do not have sufficient phase coverage, we still could use the spot model to explain their light-curve variation successfully based on the photometric solution in 2004. Comparing the light curves of 1999, 2004, and 2005, the light curve distortion changes on both short and long time scales, especially the significant variation around the secondary minimum on a time scale of two months. Analysis of the longitude of spots within the belt around 270 degrees suggests that the activity cycle of RT And may be 6.69 +/- 0.80 years.