2020ApJ...896..128M

Classical Cepheids are powerful probes of both stellar evolution and near-field cosmology thanks to their great luminosities, pulsations, and their adherence to the Leavitt (period-luminosity) Law. However, there still exist a number of questions regarding their evolution, such as the roles of rotation, convective core overshooting, and winds. ln particular, how do these processes impact Cepheid evolution and the predicted fundamental properties such as stellar mass? In this work, we compare a sample of Cepheids with measured rates of period change with new evolution models to test the impact of these first two processes. In our previous study we found that enhanced mass loss is crucial for describing the sample, and here we continue that analysis but for rotational mixing and core overshooting. We show that while rotation is important for stellar evolution studies, rotation itself is insufficient to model the distribution of period change rates from the observed sample. On the other hand, convective core overshooting is needed to explain the magnitude of the rates of period change, but does not explain the number of stars with positive and negative period change rates. In conclusion, we determine that convective core overshooting and stellar rotation alone are not enough to account for the observed distribution of Cepheid rates of period change and another mechanism, such as pulsation-driven mass loss, may be required.