Study of the contact binary AK Herculis: Light-curve analysis and orbital period investigation

AK Her is a very interesting contact binary exhibiting variable light curve s and an obvious O'Connell effect, with max I greater than max II. In the p resent work an extensive study of this system is made covering not only its light curve analysis, but also its orbital period changes in an attempt to give a definite answer regarding the apsidal motion of AK Her. Photoelectr ic observations of AK Her, obtained between 1985-1987 at the National Obser vatory of Athens Greece, are presented, analysed and discussed. The light c urve analysis was made with the W-D code and the geometric and photometric elements of the system were derived. The O'Connell effect was faced with a two dark spot model. Moreover, the orbital period of the system was examine d and two periodicities were detected. Since the first one corresponds to t he time interval for which observational data exist and the second was foun d to be half of the first, it turns out that none of them is true. Two othe r significant results that came from the present analysis are that the orbi tal period of AK Her does not follow a sinusoidal variation and that, from the times of minimum light at primary and secondary eclipses, it seems that there is no apsidal motion.