Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Refining the Oort and Galactic constants   The local stellar kinematics of the Milky Way offer a useful tool for
studying the rotation curve of the Galaxy. These kinematics -- usually
parameterized by the Oort constants A and B -- depend on the local gradient of
the rotation curve as well as its absolute value (Theta_0), and the Sun's
distance to the Galactic center (R_0). The density of interstellar gas in the
Milky Way is shown to vary non-monotonically with radius, and so contributes
significantly to the local gradient of the rotation curve. We have therefore
calculated mass models for the Milky Way that include this component, and have
derived the corresponding radial variation in the Oort constants. Between
0.9R_0 and 1.2R_0, the Oort functions, A(R) and B(R), differ significantly from
the general Theta/R dependence. Various previously-inexplicable observations
are shown to be consistent with these predictions. These models can explain the
40% difference between the values for 2 A R_0 derived from radial velocity data
originating in the inner and outer Galaxy. They also go some way toward
explaining the different shapes of the velocity ellipsoids of giant and dwarf
stars in the solar neighbourhood. However, a consistent picture only emerges if
one adopts small values of R_0 = 7.1 +/- 0.4 kpc and Theta_0 = 184 +/- 8 km/s.
With these Galactic constants, the Milky Way's rotation curve declines slowly
in the outer Galaxy; V_rot(20 kpc) = 166 kms. Our low value for R_0 agrees well
with the only direct determination (7.2 +/- 0.7 kpc, Reid 1993). Using these
Galactic constants, we find that the proper motion of Sgr A^* is consistent
with the observational constraints. The radial velocities and proper motions of
our best fit model are entirely consistent with the radial velocities of
Cepheids and the Hipparcos measurements of their proper motions.

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The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
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The categories of this paper are: quant-ph
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The categories of this paper are: comp-gas
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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: nucl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: funct-an
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The categories of this paper are: cs
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The categories of this paper are: plasm-ph
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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: gr-qc
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The categories of this paper are: q-alg
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The categories of this paper are: q-fin