Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Structure of W3(OH) from Very High Spectral Resolution Observations of 5
  Centimeter OH Masers   Recent studies of methanol and ground-state OH masers at very high spectral
resolution have shed new light on small-scale maser processes. The nearby
source W3(OH), which contains numerous bright masers in several different
transitions, provides an excellent laboratory for high spectral resolution
techniques. We present a model of W3(OH) based on EVN observations of the
rotationally-excited 6030 and 6035 MHz OH masers taken at 0.024 km/s spectral
resolution. The 6.0 GHz masers are becoming brighter with time and show
evidence for tangential proper motions. We confirm the existence of a region of
magnetic field oriented toward the observer to the southeast and find another
such region to the northeast in W3(OH), near the champagne flow. The 6.0 GHz
masers trace the inner edge of a counterclockwise rotating torus feature.
Masers at 6030 MHz are usually a factor of a few weaker than at 6035 MHz but
trace the same material. Velocity gradients of nearby Zeeman components are
much more closely correlated than in the ground state, likely due to the
smaller spatial separation between Zeeman components. Hydroxyl maser peaks at
very long baseline interferometric resolution appear to have structure on
scales both smaller than that resolvable as well as on larger scales.

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The categories of this paper are: ao-sci
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The categories of this paper are: nlin
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The categories of this paper are: chem-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: math-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: eess
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The categories of this paper are: q-fin
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The categories of this paper are: cond-mat
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The categories of this paper are: quant-ph
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The categories of this paper are: q-bio
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The categories of this paper are: supr-con
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The categories of this paper are: dg-ga
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The categories of this paper are: mtrl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: econ