Light variations of RT Lac during the last ten years

The RS CVn-type eclipsing binary star RT Lac has been observed in B and V colours, during 1984, 1985, 1986, 1987, and 1988 observing seasons. The orbital period of the system was found to be decreasing with an amount of 62 s century-1. The brightnesses both at minima and maxima are changing with time. It seems that the variations of the brightnesses at mid-primary and second quarter are similar, but at second first quarters are opposite to each other. We believe that these variations are mainly related with the spots (or spot groups) located on the surface of the component star which is in front during the primary minimum. We also estimate the period of the spot activity cycle to be approximately six years. © 1989 Kluwer Academic Publishers