The active RS Canum Venaticorum binary II Pegasi IV. The spot activity cycle

A total of 6 new surface images of II Peg obtained for the years 1997 and 1 998 confirms the recently revealed permanent active longitude structure. Th e lower limit of the active longitudes' Lifetime is now extended up to 25 y ears. A new "flip-flop" phenomenon, redefined as a switch of the activity b etween the active longitudes, has started in summer of 1998. It coincides r easonably well with the moment predicted from the activity cycle of the sta r. This confirms definitely the cyclic behaviour of the activity of II Peg we recently discovered. Therefore, we assign numbers to the cycles of 4.65 yr since the earliest photoelectric observations of II Peg and define the a ctive longitudes as "odd" and "even" corresponding to odd and even numbers of cycles. With such a definition, in late 1998 the 7th cycle began and the "odd" active longitude became more active. From the analysis of the spot a rea evolution within the active longitudes we conclude that the activity cy cle is developed as a rearrangement of the nearly constant amount of the sp ot area between the active longitudes. We discuss the "flip-flop" phenomeno n as a tracer of stellar activity and the role of the unseen secondary in e stablishing the cycle.