{
  "id": "2005.13077",
  "version": "v1",
  "published": "2020-05-26T23:03:59.000Z",
  "updated": "2020-05-26T23:03:59.000Z",
  "title": "Magnetic Field Structure of Orion Source I",
  "authors": [
    "Tomoya Hirota",
    "Richard L. Plambeck",
    "Melvyn C. H. Wright",
    "Masahiro N. Machida",
    "Yuko Matsushita",
    "Kazuhito Motogi",
    "Mi Kyoung Kim",
    "Ross A. Burns",
    "Mareki Honma"
  ],
  "comment": "71 pages, 57 figures, accepted for publication in The Astrophysical Journal",
  "categories": [
    "astro-ph.SR",
    "astro-ph.GA"
  ],
  "abstract": "We observed polarization of the SiO rotational transitions from Orion Source I (SrcI) to probe the magnetic field in bipolar outflows from this high mass protostar. Both 43 GHz $J$=1-0 and 86 GHz $J$=2-1 lines were mapped with $\\sim$20 AU resolution, using the VLA and ALMA, respectively. The $^{28}$SiO transitions in the ground vibrational state are a mixture of thermal and maser emission. Comparison of the polarization position angles in the $J$=1-0 and $J$=2-1 transitions allows us to set an upper limit on possible Faraday rotation of $10^{4}$ radians m$^{-2}$, which would twist the $J$=2-1 position angles typically by less than 10 degrees. The smooth, systematic polarization structure in the outflow lobes suggests a well ordered magnetic field on scales of a few hundred AU. The uniformity of the polarization suggests a field strength of $\\sim$30 milli-Gauss. It is strong enough to shape the bipolar outflow and possibly lead to sub-Keplerian rotation of gas at the base of the outflow. The strikingly high fractional linear polarizations of 80-90% in the $^{28}$SiO $v$=0 masers require anisotropic pumping. We measured circular polarizations of 60% toward the strongest maser feature in the $v$=0 $J$=1-0 peak. Anisotropic resonant scattering (ARS) is likely to be responsible for this circular polarization. We also present maps of the $^{29}$SiO $v$=0 $J$=2-1 maser and several other SiO transitions at higher vibrational levels and isotopologues.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-05-26T23:03:59.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "magnetic field structure",
      "orion source",
      "circular polarization",
      "position angles",
      "sio transitions"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 71,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}