The One-Zone Model of Cepheid's Pulsations by Zhevakin, Reconsidered

TL;DR

This paper reevaluates the one-zone model of Cepheid pulsations, finding that hydrodynamic effects dominate and the model fails to capture key features of observed stellar behavior.

Contribution

It revises the one-zone model by incorporating thermonuclear processes and assesses its limitations in accurately modeling Cepheid pulsations.

Findings

Hydrodynamic effects dominate in the model.

The simplified model reduces to adiabatic pulsations.

The model does not reproduce key features of Cepheid light curves.

Abstract

The one-zone model of non-adiabatic radial stellar pulsations is considered. Contrary to the original Zhevakin's work the triple-alpha process is the basic thermonuclear fusion reaction within the star under investigation. The model has four dimensionless numbers. For real Cepheids, the magnitude of each of these dimensionless numbers is estimated. It is found that dimensionless numbers associated with both radiation confinement and thermonuclear energy generation are sufficiently less than 1, that is, pure hydrodynamic effects prevail in the model studied. For this case, the model system reduces to the well-known equation of Bhatnagar and Kothari, which describes adiabatic radial pulsations. But solutions of this equation do not have many of real Cepheid curve's features (for instance, asymmetry of luminosity curves about mid-period points). Thus, the model under consideration is not satisfactory for describing Cepheid's pulsations. The problem of construction of an adequate simplified model of stellar pulsations is briefly discussed.