{
  "id": "1704.03760",
  "version": "v1",
  "published": "2017-04-12T13:57:10.000Z",
  "updated": "2017-04-12T13:57:10.000Z",
  "title": "Planar infall of CH3OH gas around Cepheus A HW2",
  "authors": [
    "A. Sanna",
    "L. Moscadelli",
    "G. Surcis",
    "H. J. van Langevelde",
    "K. J. E. Torstensson",
    "A. M. Sobolev"
  ],
  "comment": "9 pages, 4 figures, 2 tables, accepted by Astronomy & Astrophysics",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Aims: In order to test the nature of an (accretion) disk in the vicinity of Cepheus A HW2, we measured the three-dimensional velocity field of the CH3OH maser spots, which are projected within 1000au of the HW2 object, with an accuracy of the order of 0.1km/s. Methods: We made use of the European VLBI Network (EVN) to image the 6.7GHz CH3OH maser emission towards Cepheus A HW2 with 4.5 milli-arcsecond resolution (3au). We observed at three epochs spaced by one year between 2013 and 2015. During the last epoch, on mid-march 2015, we benefited from the new deployed Sardinia Radio Telescope. Results: We show that the CH3OH velocity vectors lie on a preferential plane for the gas motion with only small deviations of 12+/-9 degrees away from the plane. This plane is oriented at a position angle of 134 degrees east of north, and inclined by 26 degrees with the line-of-sight, closely matching the orientation of the disk-like structure previously reported by Patel et al.(2005). Knowing the orientation of the equatorial plane, we can reconstruct a face-on view of the CH3OH gas kinematics onto the plane. CH3OH maser emission is detected within a radius of 900au from HW2, and down to a radius of about 300au, the latter coincident with the extent of the dust emission at 0.9mm. The velocity field is dominated by an infall component of about 2km/s down to a radius of 300au, where a rotational component of 4km/s becomes dominant. We discuss the nature of this velocity field and the implications for the enclosed mass. Conclusions: These findings bring direct support to the interpretation that the high-density gas and dust emission, surrounding Cepheus A HW2, trace an accretion disk.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-04-12T13:57:10.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "planar infall",
      "velocity field",
      "dust emission",
      "ch3oh velocity vectors lie",
      "7ghz ch3oh maser emission"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 9,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}