Opacity Effects on Pulsations of A-Type Stars

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.