August 7-10, 2017

Abstract

Opacity Effects on Pulsations of A-type Stars

Joyce A. Guzik (Los Alamos National Laboratory)

Chris Fryer and Christopher J. Fontes (Los Alamos National Laboratory)

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 (see, e.g., Walczak et al. 2015, 2017; Daszynska-Daszkiewicz et al. 2017; Moravveji 2016; Cugier 2014). For these stars, the pulsations are driven by the opacity bump of Fe-group elements at ~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 ~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. In addition, many studies of the pulsation instability region for A stars show that other factors also influence the pulsations, for example, helium abundance and diffusive settling. Here we revisit some of these effects, focusing on modeling of early A type stars. We compare results using the new LANL OPLIB (Colgan et al. 2015) vs. LLNL OPAL (Iglesias and Rogers 1996) opacities for the Asplund et al. (ARA&A 2009; AGSS09) solar mixture, and consider opacity enhancements for Fe motivated by the Bailey et al. (2015) experiments. We compare results with observations for several early A-type stars, some of which have been proposed for BRITE observations

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