Search for Evolutionary Changes in the Periods of Cepheids: V1033 Cyg, a Classical Cepheid at the First Crossing of the Instability Strip
Lemasle, B.; Berdnikov, L. N.; Kniazev, A. Yu.; Pastukhova, E. N.; Bono, G.; Kovtyukh, V. V.; Usenko, I. A.; Hajdu, G.; Grebel, E.; Zhuiko, S. V.; Udovichenko, S. N.; Keir, L. E.
Russia, Ukraine, Germany, South Africa, Italy, Chile
Abstract
For the classical Cepheid V1033 Cyg we have constructed an O—C diagram spanning a time interval of 117 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 increase in the period dP/dt = 18.19 (±0.08) syr-1, in agreement with the results of theoretical calculations for the first crossing of the instability strip. Thus, V1033 Cyg is the second actually observed Cepheid (after α UMi) that crosses the instability strip for the first time.