Non-Linear Cepheid Period-Luminosity Relation and the Interaction of Stellar Photosphere with Hydrogen Ionization Front

TL;DR

This paper reviews evidence for non-linearity in the Cepheid period-luminosity relation, especially around 10 days, and proposes a theoretical explanation involving stellar photosphere and hydrogen ionization front interaction.

Contribution

It provides a comprehensive review of the linear versus non-linear P-L relation evidence and introduces a new theoretical model explaining the non-linearity.

Findings

Evidence supports non-linear P-L relation with a break around 10 days.

Theoretical explanation involves interaction between stellar photosphere and hydrogen ionization front.

Review covers optical to near-infrared bands.

Abstract

The Cepheid period-luminosity (P-L) relation is regarded as a linear relation (in log[P]) for a wide period range from ~2 to ~100 days. However, several recent controversial works have suggested that the P-L relation derived from the Large Magellanic Cloud (LMC) Cepheids exhibits a non-linear feature with a break period around 10 days. Here we review the evidence for linear/non-linear P-L relations from optical to near infrared bands. We offer a possible theoretical explanation to account for the nonlinear P-L relation from the idea of stellar photosphere - hydrogen ionization front interaction.