Classical Cepheids Require Enhanced Mass Loss

TL;DR

This study shows that incorporating enhanced mass loss in stellar models improves the agreement between predicted and observed period changes in Classical Cepheids, suggesting mass loss is a common feature.

Contribution

It provides the first large-scale evidence that enhanced mass loss is a universal property of Classical Cepheids, improving stellar evolution models.

Findings

Models with enhanced mass loss match observed period changes better.

Canonical models without mass loss do not agree with observations.

Enhanced mass loss is likely a common feature among Classical Cepheids.

Abstract

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. Our recent study of the period change of the nearest Cepheid, Polaris, suggested that it is undergoing enhanced mass loss when compared to canonical stellar evolution model predictions. In this work, we expand the analysis to rates of period change measured for about 200 Galactic Cepheids and compare them 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 yields predicted rates in better agreement with observations. This is the first evidence that enhanced mass loss as suggested previously for Polaris and delta Cephei must be a ubiquitous property of Classical Cepheids.