As displayed in the figure, the general trend of the (O − C)1 curve shows an upward parabolic change, indicating that the period is continuously increasing. However, after the long-term continuous increase was removed from the (O − C)1 curve, we found that there is a periodic variation in the residuals. Therefore, a cyclic term was added to a quadratic ephemeris to give a good fit to the observations (solid line in the upper panel of Figure 2).