Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Ap 2-1 nebula and the surrounding molecular cloud G35.2-0.74: an
  active star forming region   Using data from large-scale surveys: 2MASS, GLIMPSE, MIPSGAL, VGPS, GRS, and
IPHAS, we performed a multiwavelength study of the ISM in a region of about 20'
x 20' towards the molecular cloud G35.2-0.74. Additionally, the Ap 2-1 nebula,
that is seen in projection over the molecular cloud, was studied using optical
data obtained with the 2.15 m telescope at CASLEO, Argentina. From the HI
absorption study we estimate a distance of ~2 kpc for Ap 2-1 confirming that
the nebula is embedded in the south portion of the molecular cloud G35.2-0.74.
Performing a photometric study and analysing the spectral energy distributions
of the sources likely embedded in the cloud, we confirm that this region is
very active in star formation, mainly towards the north, where we discover a
cluster of young stellar objects. From the H_alpha and [NII] lines we obtain a
radial velocity of v_LSR ~ 31 km/s for the Ap 2-1 nebula, in coincidence with
the velocity of the molecular cloud. Finally, we conclude that Ap 2-1 is an HII
region probably excited by an early B-type star.

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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
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The categories of this paper are: cmp-lg
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The categories of this paper are: supr-con
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The categories of this paper are: hep-th
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The categories of this paper are: physics
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The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: solv-int
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The categories of this paper are: nlin
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The categories of this paper are: stat
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The categories of this paper are: chem-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: eess