{
  "id": "0907.4414",
  "version": "v1",
  "published": "2009-07-25T15:29:12.000Z",
  "updated": "2009-07-25T15:29:12.000Z",
  "title": "Excitation and abundance study of CO+ in the interstellar medium",
  "authors": [
    "Pascal Staeuber",
    "Simon Bruderer"
  ],
  "comment": "9 pages, 7 figures",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "Observations of CO+ suggest column densities on the order 10^12 cm^-2 that can not be reproduced by many chemical models. CO+ is more likely to be destroyed than excited in collisions with hydrogen. An anomalous excitation mechanism may thus have to be considered when interpreting CO^+ observations. Chemical models are used to perform a parameter study of CO^+ abundances. Line fluxes are calculated for N(CO+)=10^12 cm^-2 and different gas densities and temperatures using a non-LTE escape probability method. The chemical formation and destruction rates are considered explicitly in the detailed balance equations of the radiative transfer. In addition, the rotational levels of CO+ are assumed to be excited upon chemical formation according to a formation temperature. It is found, that chemical models are generally able to produce high fractional CO+ abundances (x(CO+) =10^-10). In a far-ultraviolet (FUV) dominated environment, however, high abundances of CO+ are only produced in regions with a Habing field G0 > 100 and T(kin) > 600 K, posing a strong constraint on the gas temperature. For gas densities >10^6 cm^-3 and temperatures > 600 K, the combination of chemical and radiative transfer analysis shows little effect on intensities of CO+ lines with upper levels N_up <= 3. Significantly different line fluxes are calculated with an anomalous excitation mechanism, however, for transitions with higher upper levels and densities >10^6 cm ^ -3. The Herschel Space Observatory is able to reveal such effects in the terahertz wavelength regime. Ideal objects to observe are protoplanetary disks with densities 10^6 cm^-3. It is finally suggested that the CO+ chemistry may be well understood and that the abundances observed so far can be explained with a high enough gas temperature and a proper geometry.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2009-07-25T15:29:12.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "interstellar medium",
      "abundance study",
      "excitation",
      "chemical models",
      "gas temperature"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1051/0004-6361/200912381",
      "journal": "Astronomy and Astrophysics",
      "year": 2009,
      "month": "Oct",
      "volume": 505,
      "number": 1,
      "pages": 195
    },
    "note": {
      "typesetting": "TeX",
      "pages": 9,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 826823,
      "adsabs": "2009A&A...505..195S"
    }
  }
}