Stellar Arrhythmias

Abstract

The light curves of the two large amplitude variable stars, R Scuti and AC Herculis, display irregular pulsation cycles with 'periods' of 75 and 35 days, respectively. We review the evidence that the observed time-series are generated by low dimensional chaotic dynamics. In particular, a global flow reconstruction technique indicates that the minimum embedding dimensions are 4 and 3 for R Sct and AC Her, respectively, whereas the fractal dimensions are inferred to be approximately 3.1 and 2.05 - 2.45, respectively. It thus appears that the dimensions of the dynamics themselves are also 4 and 3.