Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Spitzer View of Mon OB1 East/NGC 2264   We present Spitzer 3.6, 4.5, 5.8, 8.0, and 24 micron images of the Mon OB1
East giant molecular cloud, which contains the young star forming region NGC
2264, as well as more extended star formation. With Spitzer data and 2MASS
photometry, we identify and classify young stellar objects (YSOs) with dusty
circumstellar disks and/or envelopes in Mon OB1 East by their infrared-excess
emission and study their distribution with respect to cloud material. We find a
correlation between the local surface density of YSOs and column density of
molecular gas as traced by dust extinction that is roughly described as a power
law in these quantities. NGC 2264 follows a power law index of ~2.7, exhibiting
a large YSO surface density for a given gas column density. Outside of NGC 2264
where the surface density of YSOs is lower, the power law is shallower and the
region exhibits a larger gas column density for a YSO surface density,
suggesting the star formation is more recent. In order to measure the fraction
of cloud members with circumstellar disks/envelopes, we estimate the number of
diskless pre-main sequence stars by statistical removal of background star
detections. We find that the disk fraction of the NGC 2264 region is 45%, while
the surrounding more distributed regions show a disk fraction of 19%. This may
be explained by the presence an older, more dispersed population of stars. In
total, the Spitzer observations provide evidence for heterogenous, non-coeval
star formation throughout the Mon OB1 cloud.

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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
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The categories of this paper are: math
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The categories of this paper are: cond-mat
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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: quant-ph
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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: ao-sci
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The categories of this paper are: nlin
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-fin
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: econ