Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Classical Cepheids in the Galactic outer ring R1R2'   The kinematics and distribution of classical Cepheids within ~3 kpc from the
Sun suggest the existence of the outer ring R1R2' in the Galaxy. The optimum
value of the solar position angle with respect to the major axis of the bar,
theta_b, providing the best agreement between the distribution of Cepheids and
model particles is theta_b=37 +/- 13 degrees. The kinematical features obtained
for Cepheids with negative Galactocentric radial velocity VR are consistent
with the solar location near the descending segment of the outer ring R2. The
sharp rise of extinction toward of the Galactic center can be explained by the
presence of the outer ring R1 near the Sun.

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The categories of this paper are: math
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The categories of this paper are: funct-an
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The categories of this paper are: q-alg
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The categories of this paper are: alg-geom
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The categories of this paper are: stat
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The categories of this paper are: cond-mat
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: q-bio
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The categories of this paper are: acc-phys
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The categories of this paper are: comp-gas
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The categories of this paper are: plasm-ph