2002A&A...390..555Y

New timing of minimum light determined from CCD observations of the W UMa type contact binary AH Tau is presented. From the present time of minimum light and those collected from the literature, the changes in the orbital period of the system are analyzed. The result reveals that the orbital period of AH Tau continuously decreased at a rate of (Δp)/(p)=-1.4x10^–11 from 1944 to 1976 and suddenly and sharply decreased by about 0.33s around 1976. After 1976 the orbital period of the system continually increased at a change rate of (Δp)/(p)=1.5x10^–10. A possible explanation of the changes in the orbital period of AH Tau is discussed. They may be the result of compound action of three mechanisms: the cyclical magnetic activity, the mass loss and the radius swelling of the two components of the system.