Search for Evolutionary Changes in the Periods of Cepheids: CF Cas

Abstract

For the classical Cepheid CF Cas we have constructed an O-C diagram spanning a time interval of 129 years. The O-C diagram has the shape of a parabola, which has made it possible to determine for the first time the quadratic light elements and to calculate the rate of evolutionary decrease in the period, dP/dt = −0.050 (±0.006) syr⁻¹, in agreement with the results of theoretical calculations for the second crossing of the instability strip. The available data reduced by the Eddington-Plakidis method show no random period fluctuations, i.e., the parabola on the O-C diagram reflects a real evolutionary decrease in the period.