Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The structure of the Orion Nebula in the direction of Theta 1 Ori C   We have used existing optical emission and absorption lines, [C II] emission
lines, and H I absorption lines to create a new model for a Central Column of
material near the Trapezium region of the Orion Nebula. This was necessary
because recent high spectral resolution spectra of optical emission lines and
imaging spectra in the [C II] 158 micron line have shown that there are new
velocity systems associated with the foreground Veil and the material lying
between Theta 1 Ori C and the Main Ionization Front of the nebula. When a
family of models generated with the spectral synthesis code Cloudy were
compared with the surface brightness of the emission lines and strengths of the
Veil absorption lines seen in the Trapezium stars, distances from Theta 1 Ori
C, were derived, with the closest, highest ionization layer being 1.3 pc. The
line of sight distance of this layer is comparable with the size of the inner
Huygens Region in the plane of the sky. These layers are all blueshifted with
respect to the Orion Nebula Cluster of stars, probably because of the pressure
of a hot central bubble created by Theta 1 Ori C's stellar wind. We find
velocity components that are ascribed to both sides of this bubble. Our
analysis shows that the foreground [C II] 158 micron emission is part of a
previously identified layer that forms a portion of a recently discovered
expanding shell of material covering most of the larger Extended Orion Nebula.

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The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
26
The categories of this paper are: bayes-an
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The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th
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The categories of this paper are: q-alg
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The categories of this paper are: nucl-ex
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The categories of this paper are: stat
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The categories of this paper are: adap-org
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The categories of this paper are: comp-gas
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
25
The categories of this paper are: patt-sol