Overtone Pulsations Revisited

TL;DR

This paper analyzes hydrodynamical simulations of RR Lyrae and Cepheid pulsations to understand the physical origins of their light-curve differences, highlighting the limitations of morphology-based classification.

Contribution

It introduces the use of the RSP module in MESA for detailed hydrodynamical modeling of radial pulsations and compares these results with simplified one-zone models.

Findings

Light-curve shapes are influenced by complex stellar physics.

First-overtone pulsators can mimic fundamental-mode light curves.

Morphology alone is insufficient for accurate variable star classification.

Abstract

The shape of light cures of fundamental-mode and of first-overtone pulsators, as observed in RR~Lyrae variables and Cepheids, differ characteristically. The stellar physical origin of the morphological differences is not well documented and the topic seems not to be part of the elementary curriculum of students of stellar variability. To ameliorate the situation, this exposition analyzes hydrodynamical simulations of radial pulsations computed with the newly available numerical instrument RSP in MESA. The stellar physical processes that affect the light curves are identified and contrasted to the explanation based on experiments with one-zone models. The encounter of first-overtone pulsators sporting light curves that mimic those of fundamental-mode variables serves as a warning that light-curve morphology alone is not a reliable path to correctly classify pulsating variables; the exposition closes with a short discussion of constraints these modes might impose on understanding the origin of anomalous Cepheids.