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

Abstract

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 highermore » 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.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1460657
Report Number(s):
LA-UR-18-22998
Journal ID: ISSN 2218-2004; ATOMC5; TRN: US1901891
Grant/Contract Number:  
AC52-06NA25396
Resource Type:
Accepted Manuscript
Journal Name:
Atoms
Additional Journal Information:
Journal Volume: 6; Journal Issue: 2; Journal ID: ISSN 2218-2004
Publisher:
MDPI
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; stars: pulsation; stars: evolution; opacities

Citation Formats

Guzik, Joyce, Fontes, Christopher, and Fryer, Chris. Opacity Effects on Pulsations of Main-Sequence A-Type Stars. United States: N. p., 2018. Web. doi:10.3390/atoms6020031.
Guzik, Joyce, Fontes, Christopher, & Fryer, Chris. Opacity Effects on Pulsations of Main-Sequence A-Type Stars. United States. doi:10.3390/atoms6020031.
Guzik, Joyce, Fontes, Christopher, and Fryer, Chris. Mon . "Opacity Effects on Pulsations of Main-Sequence A-Type Stars". United States. doi:10.3390/atoms6020031. https://www.osti.gov/servlets/purl/1460657.
@article{osti_1460657,
title = {Opacity Effects on Pulsations of Main-Sequence A-Type Stars},
author = {Guzik, Joyce and Fontes, Christopher and Fryer, Chris},
abstractNote = {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.},
doi = {10.3390/atoms6020031},
journal = {Atoms},
number = 2,
volume = 6,
place = {United States},
year = {2018},
month = {6}
}

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