Times of maximum light for the SX Phe star XX Cyg

With the light curves derived from the new observations, we do not detect any secondary maximum in the descending portion of the light curves of XX Cyg, as reported in some previous work. Frequency analysis of the light curves confirms a fundamental frequency f_0_=7.4148cycles/day and up to 19 harmonics, 11 of which are newly detected.

However, no secondary mode of pulsation is detected from the light curves. The O-C diagram, produced from 46 newly determined times of maximum light combined with those derived from the literature, reveals a continuous period increase with the rate of (1/P)(dP/dt)=1.19(13)x10^-8^/yr. Theoretical rates of period change due to the stellar evolution were calculated with a modeling code.