Magnetic Field Structure of Orion Source i

Tomoya Hirota, Tomoya Hirota, Richard L. Plambeck, Melvyn C.H. Wright, Masahiro N. MacHida, Yuko Matsushita, Kazuhito Motogi, Mi Kyoung Kim, Mi Kyoung Kim, Ross A. Burns, Ross A. Burns, Mareki Honma, Mareki Honma, Mareki Honma

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10 Citations (Scopus)


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 ∼20 au resolution, using the Very Large Array (VLA) and Atacama Large Millimeter/Submillimeter Array (ALMA), respectively. The 28SiO 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 104 rad m-2, which would twist the J = 2-1 position angles typically by less than 10°. 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 ∼30 mG. 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 28SiO 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 is likely to be responsible for this circular polarization. We also present maps of the 29SiO v = 0 J = 2-1 maser and several other SiO transitions at higher vibrational levels and isotopologues.

Original languageEnglish
Article number157
JournalAstrophysical Journal
Issue number2
Publication statusPublished - Jun 20 2020

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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