{
  "id": "0902.4472",
  "version": "v1",
  "published": "2009-02-25T21:45:59.000Z",
  "updated": "2009-02-25T21:45:59.000Z",
  "title": "Neutral oxygen spectral line formation revisited with new collisional data: large departures from LTE at low metallicity",
  "authors": [
    "D. Fabbian",
    "M. Asplund",
    "P. S. Barklem",
    "M. Carlsson",
    "D. Kiselman"
  ],
  "comment": "19 pages, 10 figures, aa.cls v6.1 included. Accepted for publication in A&A",
  "categories": [
    "astro-ph.SR",
    "astro-ph.GA"
  ],
  "abstract": "We present a detailed study of the non-Local Thermodynamic Equilibrium (non-LTE) formation of the high-excitation neutral oxygen 777 nm triplet in MARCS model atmospheres representative of late-type stars with spectral types F to K. We carried out the calculations using the statistical equilibrium code MULTI, including estimates of the impact on elemental abundance analysis. The atomic model employed includes, in particular, recent quantum-mechanical electron collision data. We confirm that the O I triplet lines form under non-LTE conditions in late-type stars, suffering negative abundance corrections with respect to LTE. At low metallicity, large line opacity stems from triplet-quintet intersystem electron collisions, a form of coupling previously not considered or seriously underestimated. The non-LTE effects become generally severe for models (both giants and dwarfs) with higher T_eff. Interestingly, in metal-poor turn-off stars, the negative non-LTE abundance corrections tend to rapidly become more severe towards lower metallicity. When neglecting H collisions, they amount to as much as ~ 0.9 dex and ~ 1.2 dex, respectively at [Fe/H]=-3 and [Fe/H]=-3.5. Even when such collisions are included, the LTE abundance remains a serious overestimate, correspondingly by ~ 0.5 dex and ~ 0.9 dex at such low metallicities. Although the poorly known inelastic hydrogen collisions thus remain an important uncertainty, the large metallicity-dependent non-LTE effects seem to point to a resulting \"low\" (compared to LTE) [O/Fe] in metal-poor halo stars.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2009-02-25T21:45:59.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "neutral oxygen spectral line formation",
      "low metallicity",
      "collisional data",
      "large departures"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1051/0004-6361/200809640",
      "journal": "Astronomy and Astrophysics",
      "year": 2009,
      "month": "Jun",
      "volume": 500,
      "number": 3,
      "pages": 1221
    },
    "note": {
      "typesetting": "TeX",
      "pages": 19,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 814214,
      "adsabs": "2009A&A...500.1221F"
    }
  }
}