Orbital period changes and photometric study of contact binary system AK Her

UBV photometry of the W UMa type eclipsing binary AK Her is presented. Light curves analysis were carried out using W-D code to obtain physical parameters of both components. The updated O-C diagram analysis yielded the values of P=62.61±0.01 years, P=25.05±0.01 years and P=13.91±0.01 years as the modulation periodicities and the values of 2.01×10-8±2.1×10-9 days, 8.9×10-9±2.1×10-9 days and 8.3×10-9±2.1×10-9 days as amplitude of orbital period modulation respectively. The consequences of these period changes are discussed on the basis of third body and magnetic activity.