{
  "id": "1208.3202",
  "version": "v1",
  "published": "2012-08-15T20:05:40.000Z",
  "updated": "2012-08-15T20:05:40.000Z",
  "title": "Chemical Analysis of a Diffuse Cloud along a Line of Sight Toward W51: Molecular Fraction and Cosmic-Ray Ionization Rate",
  "authors": [
    "Nick Indriolo",
    "D. A. Neufeld",
    "M. Gerin",
    "T. R. Geballe",
    "J. H. Black",
    "K. M. Menten",
    "J. R. Goicoechea"
  ],
  "comment": "21 pages, 1 figure, 4 tables",
  "journal": "ApJ 758 (2012) 83",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Absorption lines from the molecules OH+, H2O+, and H3+ have been observed in a diffuse molecular cloud along a line of sight near W51 IRS2. We present the first chemical analysis that combines the information provided by all three of these species. Together, OH+ and H2O+ are used to determine the molecular hydrogen fraction in the outskirts of the observed cloud, as well as the cosmic-ray ionization rate of atomic hydrogen. H3+ is used to infer the cosmic-ray ionization rate of H2 in the molecular interior of the cloud, which we find to be zeta_2=(4.8+-3.4)x10^-16 per second. Combining the results from all three species we find an efficiency factor---defined as the ratio of the formation rate of OH+ to the cosmic-ray ionization rate of H---of epsilon=0.07+-0.04, much lower than predicted by chemical models. This is an important step in the future use of OH+ and H2O+ on their own as tracers of the cosmic-ray ionization rate.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2012-08-15T20:05:40.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "cosmic-ray ionization rate",
      "molecular fraction",
      "diffuse cloud",
      "diffuse molecular cloud",
      "molecular hydrogen fraction"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1088/0004-637X/758/2/83",
      "journal": "The Astrophysical Journal",
      "year": 2012,
      "month": "Oct",
      "volume": 758,
      "number": 2,
      "pages": 83
    },
    "note": {
      "typesetting": "TeX",
      "pages": 21,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1127664,
      "adsabs": "2012ApJ...758...83I"
    }
  }
}