Opacity Effects on Pulsations of A-Type Stars

TL;DR

This paper investigates how different opacity models affect pulsation behaviors in A-type stars, comparing LANL OPLIB and LLNL OPAL opacities, and discusses potential observational constraints from BRITE data.

Contribution

It provides a comparative analysis of opacity effects on A-type star pulsations using new opacity tables and discusses implications for observational studies.

Findings

Opacity differences influence pulsation instability regions.

Helium abundance and diffusion also affect pulsations.

BRITE observations could help constrain stellar opacities.

Abstract

The effects of opacities in driving pulsations and extending the pulsation instability region for B-type stars (SPB and $\beta$ Cep variables) have recently been explored by, e.g., Walczak et al. 2015, 2017, Daszynska-Daszkiewicz et al. 2017; Moravveji 2016, and Cugier 2014. For these stars, the pulsations are driven by the opacity bump of Fe-group elements at around 200,000 K in the stellar envelope. For $\delta$ Scuti pulsations in A-type stars, pulsations are driven instead by the $\kappa$ effect in the second helium ionization region at around 50,000 K. Opacity modifications investigated for B-type stars may also have an effect on the structure of A-type stars and the instability region. Studies of the pulsation instability region for A-type stars show that other factors also influence the pulsations, for example, helium abundance and diffusive settling. Here we explore some of these effects, focusing on modeling of A-type stars. We compare results using the new LANL OPLIB vs. LLNL OPAL opacities for the AGSS09 solar abundance mixture. We comment on prospects for using BRITE observations of A-type stars to constrain opacities.