Volume 41 number 1 (2013)
We have used AAVSO visual data, and Fourier analysis and self-correlation analysis, to study the periodicity of 55 semiregular (SR) variables - 21 SRa and 34 SRb. According to the standard system of variable star classification, these are pulsating red giants, with visual amplitudes less than 2.5 magnitudes, which show noticeable periodicity (SRa) or less-obvious periodicity (SRb). We find that their behavior ranges from highly periodic to irregular; some are not significantly variable. We have used a simple index, based on self-correlation analysis, to show that, on average, the SRa variables have a larger component of periodicity than the SRb variables, as expected. The distributions of this index for the two groups, however, overlap considerably. Of our 55 stars, 11 definitely or possibly show two radial periods, and at least 16 definitely or possibly show a long secondary period. We also analyzed three non-SR stars: T Cet is a double-mode SRc star; T Cen is an RVa star which should be reclassified as RVb; V930 Cyg is an irregular (Lb) star with a strong 250-day period.