Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spectroscopic Follow-Up of the Hercules Aquila Cloud   We designed a follow-up program to find the spectroscopic properties of the
Hercules-Aquila Cloud (HAC) and test scenarios for its formation. We measured
the radial velocities (RVs) of 45 RR Lyrae in the southern portion of the HAC
using the facilities at the MDM observatory, producing the first large sample
of velocities in the HAC. We found a double-peaked distribution in RVs, skewed
slightly to negative velocities. We compared both the morphology of HAC
projected onto the plane of the sky and the distribution of velocities in this
structure outlined by RR Lyrae and other tracer populations at different
distances to N-body simulations. We found that the behaviour is characteristic
of an old, well-mixed accretion event with small apo-galactic radius. We cannot
yet rule out other formation mechanisms for the HAC. However, if our
interpretation is correct, HAC represents just a small portion of a much larger
debris structure spread throughout the inner Galaxy whose distinct kinematic
structure should be apparent in RV studies along many lines of sight.

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The categories of this paper are: physics
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The categories of this paper are: dg-ga
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The categories of this paper are: acc-phys
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The categories of this paper are: adap-org
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The categories of this paper are: econ
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The categories of this paper are: q-fin
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-bio
35
The categories of this paper are: mtrl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-lat
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The categories of this paper are: cs
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The categories of this paper are: stat
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-alg
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The categories of this paper are: bayes-an