2001A&A...368..595L

A detailed study of the period and the light-curve of the eclipsing binary AK Her is presented. Based on the study of the (O-C) curve, we find that the period variation of the system contains a component of a long-term decrease, and three other components of periodical variation. Our result is very different from that of other investigators. We compare light curves obtained by other groups and find that the light curve of the system has changed considerably. Based on the analysis, we investigate the physical mechanisms which may underlie the variations of the period and the light curve and obtain some new conclusions. According to the characteristics of rapid light variation of the system, we conclude that the rapid change is probably caused by pulsation of the common envelope, and that the physical mechanism causing the pulsation may be mass transfer between the two components. In addition, we find that the amplitude of the light curve variation is almost proportional to the rate of the period variation. Finally, the trends in the evolution of the system are discussed.