Long-term spottedness variations of 16 RS CVn stars

An improved zonal model for spotted stellar photospheres enabling analysis of two active longitudes simultaneously present on a star is used to determine the spottedness parameters for a sample of chromospherically active RS CVn binary stars. Variations of the spot-activity characteristics of these systems with time are analyzed for time scales of several decades, in order to search for evolutionary changes of their spotted regions. The analysis made use of observations acquired during multi-color photometric monitoring of six spotted active RS CVn systems conducted at the Astronomical Observatory of the Ural Federal University and the Crimean Astrophysical Observatory since 2003, as well as data from the literature. Half of the stars display drifts of their spots towards the equator and poles during some time intervals; however, the speeds of the spots’ latitude drifts are lower than the analogous speeds for sunspots, by factors of 1.5–4, on average. Correlations or anti-correlations between a spot’s area and its latitude were detected for nine stars, with the correlation coefficients R ranging from 0.54 to 0.93; stronger correlations are found for stars whose spot areas increasewith increasing latitude during the entire analyzed time interval. Activity cycles lasting from 5 to 28 years have been determined or confirmed for nine of the studied systems.