Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: RR Lyrae Variables in NGC 2808   NGC 2808 is a unique globular cluster with not only a bimodal-horizontal
branch (HB) but also with gaps on the blue horizontal branch. Adequate
interpretation of the nature of the detected peculiarities in "bimodal" and
"gap" clusters is of paramount importance for understanding the nature of the
second parameter phenomenon and scenarios for the formation of the Galaxy.
Although RR Lyrae variables are HB stars that can provide powerful constraints
to models on the origin of bimodal HBs, unfortunately, until recently, only one
RR Lyrae variable was known in this cluster. Here we present the first
calibrated time-series CCD photometry for newly discovered fundamental mode RR
Lyrae variables in NGC 2808, with observations over a range of twenty years.
Investigations of RR Lyrae variable stars in this peculiar, bimodal-horizontal
branch globular cluster are carried out to account for its formation, and the
effects of helium enrichment and differential reddening. The Oosterhoff
classification of NGC$\,$2808, which has recently been associated with a
previously unknown dwarf galaxy in Canis Major, is also discussed.

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The categories of this paper are: eess
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The categories of this paper are: solv-int
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The categories of this paper are: supr-con
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The categories of this paper are: ao-sci
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The categories of this paper are: chem-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: cond-mat
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The categories of this paper are: math
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The categories of this paper are: comp-gas
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-th
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-ph
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The categories of this paper are: math-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: quant-ph