A Photometric Analysis of ZZ Ceti Stars: A Parameter-Free Temperature Indicator?

TL;DR

This study analyzes optical and infrared photometry of ZZ Ceti stars to propose a parameter-free method for determining their effective temperatures, comparing photometric and spectroscopic results to refine the instability strip boundaries.

Contribution

It introduces a model atmosphere analysis showing that energy distributions are insensitive to certain parameters, enabling a parameter-free temperature indicator for ZZ Ceti stars.

Findings

Photometric temperatures align well with spectroscopic values.

Energy distributions are insensitive to surface gravity and convective efficiency.

Results aid in defining the empirical boundaries of the ZZ Ceti instability strip.

Abstract

We present a model atmosphere analysis of optical VRI and infrared JHK photometric data of about two dozen ZZ Ceti stars. We first show from a theoretical point of view that the resulting energy distributions are not particularly sensitive to surface gravity or to the assumed convective efficiency, a result which suggests a parameter-free effective temperature indicator for ZZ Ceti stars. We then fit the observed energy distributions with our grid of model atmospheres and compare the photometric effective temperatures with the spectroscopic values obtained from fits to the hydrogen line profiles. Our results are finally discussed in the context of the determination of the empirical boundaries of the ZZ Ceti instability strip.