{
  "id": "1710.01027",
  "version": "v1",
  "published": "2017-10-03T08:32:32.000Z",
  "updated": "2017-10-03T08:32:32.000Z",
  "title": "Circumstellar ammonia in oxygen-rich evolved stars",
  "authors": [
    "K. T. Wong",
    "K. M. Menten",
    "T. Kamiński",
    "F. Wyrowski",
    "J. H. Lacy",
    "T. K. Greathouse"
  ],
  "comment": "38 pages, 28 figures, 6 tables, accepted for publication in Astronomy and Astrophysics, cross-listed to astro-ph.GA as per request by arXiv",
  "categories": [
    "astro-ph.SR",
    "astro-ph.GA"
  ],
  "abstract": "The circumstellar ammonia (NH$_3$) chemistry in evolved stars is poorly understood. Previous observations and modelling showed that NH$_3$ abundance in oxygen-rich stars is several orders of magnitude above that predicted by equilibrium chemistry. In this article, we characterise the spatial distribution and excitation of NH$_3$ in the O-rich circumstellar envelopes (CSEs) of four diverse targets: IK Tau, VY CMa, OH 231.8+4.2, and IRC +10420 with multi-wavelength observations. We observed the 1.3-cm inversion line emission with the Very Large Array (VLA) and submillimetre rotational line emission with the Heterodyne Instrument for the Far-Infrared (HIFI) aboard Herschel from all four targets. For IK Tau and VY CMa, we observed the rovibrational absorption lines in the $\\nu_2$ band near 10.5 $\\mu$m with the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). We also attempted to search for the rotational transition within the $v_2=1$ state near 2 mm with the IRAM 30m Telescope towards IK Tau. Non-LTE radiative transfer modelling, including radiative pumping to the vibrational state, was carried out to derive the radial distribution of NH$_3$ in these CSEs. Our modelling shows that the NH$_3$ abundance relative to molecular hydrogen is generally of the order of $10^{-7}$, which is a few times lower than previous estimates that were made without considering radiative pumping and is at least 10 times higher than that in the C-rich CSE of IRC +10216. Incidentally, we also derived a new period of IK Tau from its $V$-band light curve. NH$_3$ is again detected in very high abundance in O-rich CSEs. Its emission mainly arises from localised spatial-kinematic structures that are probably denser than the ambient gas. Circumstellar shocks in the accelerated wind may contribute to the production of NH$_3$. (Abridged abstract)",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-10-03T08:32:32.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "oxygen-rich evolved stars",
      "circumstellar ammonia",
      "ik tau",
      "texas echelon cross echelle spectrograph",
      "vy cma"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 38,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}