Long-term variability of the SX Phoenicis star CY Aquarii

We present 23 new times of maximum light of the SX Phoenicis star CY Aquarii. The O-C diagram reveals a new value of the period ...since 1996. CY Aqr is the first SX Phe star where the major component of the long-term period change can be represented without invoking large-amplitude period jumps. A linear period change combined with the light-time effect in a highly-eccentric orbit yields a reasonably precise solution. The binary explanation, however, does not account for the full magnitude of the period changes, and small residuals in the time interval 1930-1950 seem to remain.