Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Palomar 13: An Unusual Stellar System in the Galactic Halo   We have measured Keck/HIRES radial velocities for 30 candidate red giants in
the direction of Palomar 13: an object traditionally cataloged as a compact,
low-luminosity globular cluster. From a sample of 21 confirmed members, we find
a systemic velocity of 24.1 km/s and a projected, intrinsic velocity dispersion
of 2.2 km/s. Although small, this dispersion is several times larger than that
expected for a globular cluster of this luminosity and central concentration.
Taken at face value, this dispersion implies a mass-to-light ratio of ~ 40 (in
solar units) based on the best-fit King-Michie model. The surface density
profile of Palomar 13 also appears to be anomalous among Galactic globular
clusters -- depending upon the details of background subtraction and
model-fitting, Palomar 13 either contains a substantial population of
"extra-tidal" stars, or it is far more spatially extended than previously
suspected. The full surface density profile is equally well-fit by a
King-Michie model having a high concentration and large tidal radius, or by a
NFW model. We examine -- and tentatively reject -- a number of possible
explanations for the observed characteristics of Palomar 13 (e.g., velocity
"jitter" among the red giants, spectroscopic binary stars, non-standard mass
functions, modified Newtonian dynamics), and conclude that the two most
plausible scenarios are either catastrophic heating during a recent
perigalacticon passage, or the presence of a massive dark halo. Thus, the
available evidence suggests that Palomar 13 is either a globular cluster which
is now in the process of dissolving into the Galactic halo, or a faint,
dark-matter-dominated stellar system (ABRIDGED).

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The categories of this paper are: quant-ph
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The categories of this paper are: physics
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The categories of this paper are: nucl-ex
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The categories of this paper are: math
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The categories of this paper are: hep-ex
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The categories of this paper are: supr-con
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The categories of this paper are: funct-an
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The categories of this paper are: nlin
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: cond-mat
30
The categories of this paper are: q-alg
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The categories of this paper are: econ
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The categories of this paper are: adap-org