{
  "id": "1412.4818",
  "version": "v1",
  "published": "2014-12-15T22:02:54.000Z",
  "updated": "2014-12-15T22:02:54.000Z",
  "title": "Observations of water with Herschel/HIFI toward the high-mass protostar AFGL 2591",
  "authors": [
    "Y. Choi",
    "F. F. S. van der Tak",
    "E. F. van Dishoeck",
    "F. Herpin",
    "F. Wyrowski"
  ],
  "comment": "Accepted for publication in A&A",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Water is a sensitive tracer of physical conditions in star-forming regions because of its large abundance variations between hot and cold regions. We use spectrally resolved observations of rotational lines of H$_2$O and its isotopologs with Herschel/HIFI to constrain the physical conditions of the water emitting region toward the high-mass protostar AFGL2591. We use analytical estimates and rotation diagrams to estimate T$_{ex}$ and column densities of H$_2$O of the envelope, the outflow, and a foreground cloud. Furthermore, we use the non-LTE radiative transfer code to estimate the temperature and volume density of the H$_2$O emitting gas. Assuming LTE, we estimate an T$_{ex}$ of 42 K and a column density of 2$\\times$10$^{14}$ cm$^{-2}$ for the envelope and 45 K and 4$\\times$10$^{13}$ cm$^{-2}$ for the outflow, in beams of 4\" and 30\", respectively. Non-LTE models indicate a kinetic temperature of 60-230 K and a volume density of 7$\\times$10$^6$-10$^8$ cm$^{-3}$ for the envelope, and a kinetic temperature of 70-90 K and a gas density of 10$^7$-10$^8$ cm$^{-3}$ for the outflow. The o/p ratio of the foreground absorption is 1.9$\\pm$0.4, suggesting a low temperature. In contrast, the o/p ratio seen in absorption by the outflow is 3.5$\\pm$1.0, as expected for warm gas. The water abundance in the envelope is 10$^{-9}$, similar to the low values found for other high- and low-mass protostars, suggesting that this abundance is constant during the embedded phase of high-mass star formation. The water abundance in the outflow is 10$^{-10}$, which is 10$\\times$ lower than in the envelope and in the outflows of high- and low-mass protostars. Since beam size effects can only increase this estimate by a factor of 2, we suggest that the water in the outflow is affected by dissociating UV radiation due to the low extinction in the outflow lobe.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-12-15T22:02:54.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "observations",
      "herschel/hifi",
      "kinetic temperature",
      "column density",
      "volume density"
    ],
    "publication": {
      "doi": "10.1051/0004-6361/201322717",
      "journal": "Astronomy and Astrophysics",
      "year": 2015,
      "month": "Apr",
      "volume": 576
    },
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2015A&A...576A..85C"
    }
  }
}