Opacity Effects on Pulsations of Main-Sequence A-Type Stars

Guzik, Joyce; Fontes, Christopher; Fryer, Chris

doi:10.3390/atoms6020031

Title: Opacity Effects on Pulsations of Main-Sequence A-Type Stars

Journal Article · Mon Jun 04 00:00:00 EDT 2018 · Atoms

DOI:https://doi.org/10.3390/atoms6020031· OSTI ID:1460657

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Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Here, opacity enhancements for stellar interior conditions have been explored to explain observed pulsation frequencies and to extend the pulsation instability region for B-type main-sequence variable stars. For these stars, the pulsations are driven in the region of the opacity bump of Fe-group elements at ~200,000 K in the stellar envelope. Here we explore effects of opacity enhancements for the somewhat cooler main-sequence A-type stars, in which p-mode pulsations are driven instead in the second helium ionization region at ~50,000 K. We compare models using the new LANL OPLIB vs. LLNL OPAL opacities for the AGSS09 solar mixture. For models of two solar masses and effective temperature 7600 K, opacity enhancements have only a mild effect on pulsations, shifting mode frequencies and/or slightly changing kinetic-energy growth rates. Increased opacity near the bump at 200,000 K can induce convection that may alter composition gradients created by diffusive settling and radiative levitation. Opacity increases around the hydrogen and 1st He ionization region (~13,000 K) can cause additional higher-frequency p modes to be excited, raising the possibility that improved treatment of these layers may result in prediction of new modes that could be tested by observations. New or wider convective zones and higher convective velocities produced by opacity increases could also affect angular momentum transport during evolution. More work needs to be done to quantify the effects of opacity on the boundaries of the pulsation instability regions for A-type stars.

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Research Organization:: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), High Energy Physics (HEP)

Grant/Contract Number:: AC52-06NA25396

OSTI ID:: 1460657

Report Number(s):: LA-UR-18-22998; ATOMC5; TRN: US1901891

Journal Information:: Atoms, Vol. 6, Issue 2; ISSN 2218-2004

Publisher:: MDPICopyright Statement

Country of Publication:: United States

Language:: English

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