{
  "id": "1709.09435",
  "version": "v1",
  "published": "2017-09-27T10:32:15.000Z",
  "updated": "2017-09-27T10:32:15.000Z",
  "title": "The extended molecular envelope of the asymptotic giant branch star $π^{1}$ Gruis as seen by ALMA I. Large-scale kinematic structure and CO excitation properties",
  "authors": [
    "L. Doan",
    "S. Ramstedt",
    "W. H. T. Vlemmings",
    "S. Höfner",
    "E. De Beck",
    "F. Kerschbaum",
    "M. Lindqvist",
    "M. Maercker",
    "S. Mohamed",
    "C. Paladini",
    "M. Wittkowski"
  ],
  "journal": "A&A, Volume 605, September 2017",
  "doi": "10.1051/0004-6361/201730703",
  "categories": [
    "astro-ph.SR",
    "astro-ph.GA"
  ],
  "abstract": "The S-type asymptotic giant branch (AGB) star $\\pi^{1}$ Gruis has a known companion at a separation of $\\approx$400 AU. The envelope structure, including an equatorial torus and a fast bipolar outflow, is rarely seen in the AGB phase and is particularly unexpected in such a wide binary system. Therefore a second, closer companion has been suggested, but the evidence is not conclusive. The new ALMA $^{12}$CO and $^{13}$CO $J$=3-2 data, together with previously published $^{12}$CO $J$=2-1 data from the Submillimeter Array (SMA), and the $^{12}$CO $J$=5-4 and $J$=9-8 lines observed with Herschel/Heterodyne Instrument for the Far-Infrared (HIFI), is modeled with the 3D non-LTE radiative transfer code SHAPEMOL. The data analysis clearly confirms the torus-bipolar structure. The 3D model of the CSE that satisfactorily reproduces the data consists of three kinematic components: a radially expanding torus with velocity slowly increasing from 8 to 13 km s$^{-1}$ along the equator plane; a radially expanding component at the center with a constant velocity of 14 km s$^{-1}$; and a fast, bipolar outflow with velocity proportionally increasing from 14 km s$^{-1}$ at the base up to 100 km s$^{-1}$ at the tip, following a linear radial dependence. The results are used to estimate an average mass-loss rate during the creation of the torus of 7.7$\\times$10$^{-7}$ M$_{\\odot}$ yr$^{-1}$. The total mass and linear momentum of the fast outflow are estimated at 7.3$\\times$10$^{-4}$ M$_{\\odot}$ and 9.6$\\times$10$^{37}$ g cm s$^{-1}$, respectively. The momentum of the outflow is in excess (by a factor of about 20) of what could be generated by radiation pressure alone, in agreement with recent findings for more evolved sources. The best-fit model also suggests a $^{12}$CO/$^{13}$CO abundance ratio of 50. Possible shaping scenarios for the gas envelope are discussed",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-09-27T10:32:15.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "asymptotic giant branch star",
      "large-scale kinematic structure",
      "extended molecular envelope",
      "excitation properties",
      "non-lte radiative transfer code"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}