Period-color and amplitude-color relations in classical Cepheid variables V: The Small Magellanic Cloud Cepheid models

TL;DR

This study models and compares period-color and amplitude-color relations of SMC Cepheids, revealing general agreement with observations and proposing a physical mechanism involving hydrogen ionization front interactions to explain period-dependent behaviors.

Contribution

The paper introduces detailed hydrodynamic models for SMC Cepheids and explains PC/AC relations through hydrogen ionization front interactions, linking them to the period-luminosity relation.

Findings

Models agree with observations for long-period Cepheids.

Discrepancies exist for short-period Cepheids.

Proposed mechanism explains PC/AC and PL relations across galaxies.

Abstract

Period-colour (PC) and amplitude-colour (AC) relations at maximum, mean and minimum light are constructed from a large grid of full amplitude hydrodynamic models of Cepheids with a composition appropriate for the SMC (Small Magellanic Cloud). We compare these theoretical relations with those from observations. The theoretical relations are in general good agreement with their observational counterparts though there exist some discrepancy for short period (log [P] < 1) Cepheids. We outline a physical mechanism which can, in principle, be one factor to explain the observed PC/AC relations for the long and short period Cepheids in the Galaxy, LMC and SMC. Our explanation relies on the hydrogen ionization front-photosphere interaction and the way this interaction changes with pulsation period, pulsation phase and metallicity. Since the PC relation is connected with the period-luminosity (PL) relation, it is postulated that such a mechanism can also explain the observed properties of the PL relation in these three galaxies.