{
  "id": "1806.06743",
  "version": "v1",
  "published": "2018-06-18T14:49:32.000Z",
  "updated": "2018-06-18T14:49:32.000Z",
  "title": "Opacity Effects on Pulsations of Main-Sequence A-Type Stars",
  "authors": [
    "Joyce A. Guzik",
    "Christopher J. Fontes",
    "Chris Fryer"
  ],
  "comment": "14 pages, 12 figures. Accepted version for MDPI Atoms Special Issue \"Atomic and Molecular Opacity Data for Astrophysics\", Published 4 June 2018, Atoms 2018, 6(2), 31, https://doi.org/10.3390/atoms6020031",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "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 $\\sim$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 $\\sim$50,000 K. We compare models using the new LANL OPLIB vs. LLNL OPAL opacities for the AGSS09 solar mixture. For models of 2 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.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-06-18T14:49:32.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "opacity effects",
      "changing kinetic-energy growth rates",
      "pulsation instability region",
      "opacity enhancements",
      "somewhat cooler main-sequence a-type stars"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 14,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}