Aims:The rapidly rotating active stars FK Com and HD 199178 are investigated using extensive long-term photometry. The data set includes previously unpublished photometry, obtained at the Rozhen National Astronomical Observatory. We look for periodicities in the long-term photometric behaviour of both stars, as well as for spots, using light curve modelling. Special attention is paid to the behaviour of the "flip-flop" phenomenon.
Methods: Light curves in UBV of FK Com and HD 199178 are used to construct an O-C diagram for each star, and they are modelled to obtain spot distribution.
Results: The main result for FK Com is that the "flip-flop" phenomenon is a superposition of an oscillating process of activity and real and fast "flip-flops". For the oscillating component, we obtained a cycle of 5.8 years. The same cycle is also present in other photometric characteristics. The O-C diagram for HD 199178 shows a cycle of 4.2 years. Modelling of the light curves of both stars reveals a large high-latitude spot on each star and also smaller spots in the equatorial belt or at intermediate latitudes.
Tables 2, 3, and 5 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/467/229