THE NATURE OF THE PERIOD CHANGES IN RV TAURI STARS

We have studied the period changes in 15 RV Tauri stars, using the Edd ington-Piakidis hypothesis, which assumes that the (O-C) diagrams can be interpreted as a superposition of random errors in the measured tim es of minimum, and random cycle-to-cycle fluctuations in the period. E xcept far three stars for which the data are sparse, the hypothesis fi ts the (O-C) data very well, suggesting that the assumptions ate corre ct. The magnitude of the random period fluctuations does not appear to correlate with any obvious physical property of the stars.