Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Search for Stellar Populations in High Velocity Clouds   We report the results of a photometric search for giant stars associated with
the cores of four high velocity clouds (HVCs) -- two of which are compact HVCs
-- using the Las Campanas Du Pont 2.5 meter and Cerro Tololo Blanco 4 meter
telescopes in combination with a system of filters (Washington M, T_2 + DDO51)
useful for identifying low surface gravity, evolved stars. Identical
observations of nearby control fields provide a measure of the ``giant star''
background. Our data reach M_0=22 for three of the HVCs and M_0=21.25 for the
fourth, depths that allow the detection of any giant stars within 600 kpc.
Although we identify a number of faint late-type giant star candidates, we find
neither a coherent red giant branch structure nor a clear excess of giant
candidate counts in any HVC. This indicates that the giant candidates are
probably not related to the HVCs and are more likely to be either random Milky
Way giant stars or one of several classes of potential survey contaminants.
Echelle spectroscopy of the brightest giant candidates in one HVC and its
control field reveal radial velocities representative of the canonical Galactic
stellar populations. In addition to these null results, no evidence of any
young HVC stellar populations -- represented by blue main sequence stars -- is
found, a result consistent with previous searches. Our methodology,
specifically designed to find faint diffuse stellar populations, places the
tightest upper limit yet on the total stellar mass of HVCs of a few 10^5
M_{\sun}.

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The categories of this paper are: stat
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The categories of this paper are: comp-gas
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The categories of this paper are: chem-ph
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The categories of this paper are: acc-phys
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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-bio
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The categories of this paper are: adap-org
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The categories of this paper are: alg-geom
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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: physics
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The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
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The categories of this paper are: cond-mat
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The categories of this paper are: cs