Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Spectroscopic Study of the Ancient Milky Way: F- and G-Type Stars in
  the Third Data Release of the Sloan Digital Sky Survey   (Abridged) We perform an analysis of spectra and photometry for 22,770 stars
included in the third data release (DR3) of the SDSS. We measure radial
velocities and, based on a model-atmosphere analysis, derive estimates ofthe
atmospheric parameters (effective temperature, surface gravity, and [Fe/H]) for
each star. Stellar evolution models are then used to estimate distances. The
SDSS sample covers a range in stellar brightness of 14 < V < 22, and comprises
large numbers of F- and G-type stars from the thick-disk and halo populations
(up to 100 kpc from the galactic plane), therefore including some of the oldest
stars in the Milky Way. In agreement with previous results from the literature,
we find that halo stars exhibit a broad range of iron abundances, with a peak
at [Fe/H] ~ -1.4. This population exhibits essentially no galactic rotation.
Thick-disk G-dwarf stars at distances from the galactic plane in the range
1<|z|<3 kpc show a much more compact metallicity distribution, with a maximum
at [Fe/H] ~ -0.7, and a median galactic rotation velocity at that metallicity
of 157 +/- 4 km/s (a lag relative to the thin disk of 63 km/s). A comparison of
color indices and metal abundances with isochrones indicates that no
significant star formation has taken place in the halo in the last ~ 11 Gyr,
but there are thick-disk stars which are at least 2 Gyr younger. We find the
metallicities of thick-disk stars to be nearly independent of galactocentric
distance between 5 and 14 kpc, in contrast with the marked gradients found in
the literature for the thin disk. No vertical metallicity gradient is apparent
for the thick disk, but we detect a gradient inits rotational velocity of -16
+/- 4 km/s/kpc between 1 and 3 kpc from the plane.

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The categories of this paper are: cmp-lg
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The categories of this paper are: adap-org
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The categories of this paper are: hep-th
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The categories of this paper are: q-alg
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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-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: bayes-an
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The categories of this paper are: math-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: quant-ph
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The categories of this paper are: econ
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The categories of this paper are: funct-an
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The categories of this paper are: chem-ph
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The categories of this paper are: nlin