SIMBAD references

It has been known since the pioneering work of Eddington & Plakidis that the period changes in Mira stars are dominated by the effects of random cycle-to-cycle fluctuations in period, at least in the limited sample of stars that were studied. We have extended their work, using a portion of the American Association of Variable Star Observers (AAVSO) international database of variable star observations: times and magnitudes of maximum and minimum magnitude of 391 bright Mira stars over 75 yr (Kowalsky et al.). The Eddington & Plakidis model fits the data in almost every case, at least over a time interval of several tens of cycles. There is a weak correlation between the fractional period fluctuation, per cycle, and the period (or color) of the star, but not with the amplitude or chemical type (M, S, or C).