Stellar Evolution Models of Classical Cepheids Require Enhanced Mass Loss

Measurements of rates of period change of Classical Cepheids probe stellar physics and evolution. Additionally, better understanding of Cepheid structure and evolution provides greater insight into their use as standard candles and tools for measuring the Hubble constant. In this work, we compare rates of period change measured for about 200 Galactic Cepheids to population synthesis models of Cepheids including convective core overshooting and enhanced mass loss. Rates of period change predicted from stellar evolution models without mass loss do not agree with observed rates whereas including enhanced mass loss yield predicted rates in better agreement with observations. The results suggest that enhanced mass loss must be a ubiquitous property of Classical Cepheids.