On the period variations in AR Lacertae

Examination of 18 light curves, obtained between 1926 and 1974, shows that there is a wave-like distortion outside eclipse which migrates towards decreasing orbital phase at a rate which varies between 10 or 15 yrlcycle and 50 or 60 yrlcycle. The wave amplitude (max to min, in the blue) varies between about 0". 1 and 0".04. Examination of the 0 - C curve between 1900 and 1972 shows that two obvious period decreases (1932 and 1966) and one obvious increase (1957) occurred when the minimum of the wave was at O .2S and O .7 5, respectively. This same correlation has been established or suspected in RS CVn, SS Cam, RT Lac, CG Cyg, and V47 1 Tau. Extrapolation of the migration curve would indicate that AR Lac experienced a second period increase around 1974+3.