Opacity Effects on Pulsations of A-Type Stars

Joyce A. Guzik, Chris Fryer and Christopher J. Fontes

The effects of opacities in driving pulsations and extending the pulsation instability region for B-type stars (SPB and β Cep variables) have recently been explored (see, e.g., Walczak et al., 2015, 2017; Daszyńska-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 δ Scuti pulsations in A-type stars, pulsations are driven instead by the κ 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. 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 (Colgan et al., 2016) vs. LLNL OPAL (Iglesias & Rogers, 1996) opacities for the Asplund et al. (2009) solar mixture. We comment on prospects for using BRITE observations of A-type stars to constrain opacities.

Proceedings of the Polish Astronomical Society, vol. 8, 59-63 (2018)

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