Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Comparative Astrochemical Study Of The High-Mass Protostellar Objects
  NGC 7538 IRS 9 and IRS 1   We report the results of a spectroscopic study of the high-mass protostellar
object NGC 7538 IRS 9 and compare our observations to published data on the
nearby object NGC 7538 IRS 1. Both objects originated in the same molecular
cloud and appear to be at different points in their evolutionary histo- ries,
offering an unusual opportunity to study the temporal evolution of envelope
chemistry in objects sharing a presumably identical starting composition.
Observations were made with the Texas Echelon Cross Echelle Spectrograph
(TEXES), a sensitive, high spectral resolution (R = {\lambda}/{\Delta}{\lambda}
\simeq 100,000) mid-infrared grating spectrometer. Forty-six individual lines
in vibrational modes of the molecules C2H2, CH4, HCN, NH3 and CO were detected,
including two isotopologues (13CO, 12C18O) and one combination mode ({\nu}4 +
{\nu}5 C2H2). Fitting synthetic spectra to the data yielded the Doppler shift,
excitation temperature, Doppler b parameter, column density and covering factor
for each molecule observed; we also computed column density upper limits for
lines and species not detected, such as HNCO and OCS. We find differences among
spectra of the two objects likely attributable to their differing radiation and
thermal environments. Temperatures and column densities for the two objects are
generally consistent, while the larger line widths toward IRS 9 result in less
saturated lines than those toward IRS 1. Finally, we compute an upper limit on
the size of the continuum-emitting region (\sim2000 AU) and use this constraint
and our spectroscopy results to construct a schematic model of IRS 9.

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The categories of this paper are: cmp-lg
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The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
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The categories of this paper are: nucl-ex
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The categories of this paper are: stat
5
The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn
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The categories of this paper are: dg-ga
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The categories of this paper are: q-fin
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The categories of this paper are: atom-ph
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The categories of this paper are: q-alg
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The categories of this paper are: chem-ph
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The categories of this paper are: funct-an
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The categories of this paper are: nucl-th
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The categories of this paper are: physics
9
The categories of this paper are: nlin