1996A&A...314..153J

Nonparametric methods to search for periodicity in a weighted or nonweighted time point series are applied to the central meridian passage epochs of starspots on four chromospherically active stars: λ Andromedae, σ Geminorum, II Pegasi and V 711 Tauri. The rotation periods of the active longitudes for these objects are uniquely determined, regardless of the presence of differential rotation and phase shifts of the centres of main activity. The temporal changes of the long-term distribution of the starspots in one of these objects, σ Geminorum, resembles the "flip flop" phenomenon detected earlier only in FK Comae Berenices.