UVB photometry of the RS CVn-type binary HK Lacertae

We present new UBV photometry of the long-period RS CVn-type binary HK Lacertae carried out in 1981 and 1982. Although there are gaps in the data, we covered about six complete cycles each in 1981 and 1982. The shape, maximum and minimum levels, amplitude, mean brightness, asymmetry-and period of the light curve all show strong variations. The oscillations in the photometric period seem undoubtable due to the varying asymmetry in the light curve. The color-independent, complex light variation was interpreted in terms of the rearrangement of two magnetically active regions without any sizeable variation of the activity level on the surface of the visible component. Probable small increase in amplitude towards shorter wavelenghts was thought to be due to brightening by the plage effect