2001MNRAS.325.1383H

We describe the derivation of periodicities from visual data for long-period variables, and give expected errors for the derived amplitude, phase and frequency. We extend this analysis by using a moving window to deduce variation in phase and amplitude over time. The method is demonstrated on the Mira-type variable T Cas, and shows evidence that the phase of the first harmonic (period 222.4d) varies relative to the fundamental (period 444.8d) with a period of approximately 3000d. Our analysis parallels, but is completely independent of, the work of (Szatmáry, Gál & Kiss]) and (Bedding et al.]), who both use an approach based on wavelet analysis.