Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetic Field Morphology of Orion-IRc2 from 86 GHz SiO Maser
  Polarization Images   In an attempt to probe the magnetic field morphology near the massive young
star Orion-IRc2, we mapped the linear polarization of its J=2-1 SiO masers, in
both the v=0 and v=1 vibrational levels, with 0.5 arcsec resolution. The
intense v=1 masers are confined to a narrow zone 40 AU from the star. Their
polarization position angles vary significantly on time scales of years. For
the v=1 masers the stimulated emission rate R is likely to exceed the Zeeman
splitting g\Omega due to any plausible magnetic field; in this case the maser
polarization need not correlate with the field direction. The much weaker v=0
masers in the ground vibrational level lie 100-700 AU from IRc2, in what
appears to be a flared disk. Their fractional polarizations are as high as 50%.
The polarization position angles vary little across the line profile or the
emission region, and appear to be stable in time. The position angle, P.A. = 80
degrees, we measure for the J=2-1 masers differs by 70 degrees from that
measured for the J=1-0 SiO transition, possibly because of Faraday rotation in
the foreground, Orion A, HII region. A rotation measure RM = 3.3 \times 10^4
rad m$^{-2}$ is required to bring the J=2-1 and J=1-0 position angles into
concordance. The intrinsic polarization position angle for both transitions is
then 57 degrees, parallel to the plane of the putative disk. Probably the
magnetic field threads the disk poloidally. There is little evidence for a
pinched or twisted field near the star.

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The categories of this paper are: cmp-lg
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The categories of this paper are: chao-dyn
0
The categories of this paper are: hep-ph
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The categories of this paper are: adap-org
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The categories of this paper are: math-ph
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The categories of this paper are: stat
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The categories of this paper are: comp-gas
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The categories of this paper are: solv-int
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The categories of this paper are: bayes-an
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The categories of this paper are: patt-sol
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The categories of this paper are: mtrl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: cs
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The categories of this paper are: ao-sci
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-bio