Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Wide-field High-precision CCD Photometry of omega Centauri and Its RR
  Lyrae Stars   We present wide-field and high-precision BV and Ca & Stromgren by photometry
of omega Centauri and its RR Lyrae stars, which represents one of the most
extensive photometric surveys to date for this cluster. The member stars of
omega Cen are well discriminated from foreground Galactic disk stars from the
different distributions in the hk [=(Ca-b)-(b-y)] vs. b-y diagram. The
color-magnitude diagrams show the presence of several distinct red-giant
branches with a red, metal-rich, sequence clearly separated from other bluer
metal-poor ones. Comparison with our population models suggests the most
metal-rich population is few billion years younger than the most metal-poor
population. From our new BV photometry and hk metallicity measurements for RR
Lyrae stars in omega Cen, we also confirm that the luminosity of RR Lyrae stars
depends on evolutionary status as well as metallicity. From the presence of
several distinct populations and the internal age-metallicity relation, we
conclude omega Cen was once part of a more massive system that merged with the
Milky Way, as the Sagittarius dwarf galaxy is in the process of doing now.

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The categories of this paper are: chem-ph
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The categories of this paper are: q-alg
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The categories of this paper are: atom-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-bio
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The categories of this paper are: bayes-an
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The categories of this paper are: ao-sci
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The categories of this paper are: alg-geom
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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: adap-org
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The categories of this paper are: hep-th
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The categories of this paper are: comp-gas
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The categories of this paper are: plasm-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: gr-qc