Rotation, convective core overshooting, and period changes in classical Cepheid stellar evolution models

TL;DR

This study investigates how rotation and convective core overshooting influence Cepheid stellar evolution and period changes, finding that these processes alone cannot fully explain observed period change distributions.

Contribution

The paper compares models with rotation and overshooting to observed period changes, highlighting the need for additional mechanisms like pulsation-driven mass loss.

Findings

Rotation alone cannot explain period change distributions.

Convective core overshooting explains magnitude but not sign distribution.

Additional mechanisms are likely needed to match observations.

Abstract

Classical Cepheids are powerful probes of both stellar evolution and near-field cosmology thanks to their high luminosities, pulsations, and that they follow the Leavitt (Period-Luminosity) Law. However, there still exist a number of questions regarding their evolution, such as the role 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 period change that are real-time observations of stellar evolution 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.