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 Pmod1=62.61±0.01Pmod1=62.61±0.01 years, Pmod2=25.05±0.01Pmod2=25.05±0.01 years and Pmod3=13.91±0.01Pmod3=13.91±0.01 years as the modulation periodicities and the values of 2.01×10-8±2.1×10-92.01×10-8±2.1×10-9 days, 8.9×10-9±2.1×10-98.9×10-9±2.1×10-9 days and 8.3×10-9±2.1×10-98.3×10-9±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.