2020ApJ...896..157H -
Astrophys. J., 896, 157-157 (2020/June-3)
Magnetic field structure of Orion Source I.
HIROTA T., PLAMBECK R.L., WRIGHT M.C.H., MACHIDA M.N., MATSUSHITA Y., MOTOGI K., KIM M.K., BURNS R.A. and HONMA M.
Abstract (from CDS):
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.
Abstract Copyright:
© 2020. The American Astronomical Society. All rights reserved.
Journal keyword(s):
Stellar jets - Astrophysical masers - Silicon monoxide masers - Star formation - Polarimetry - Massive stars - Interferometers
Simbad objects:
11
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