Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: RR Lyrae Variables in M31 and M33   The properties of RR Lyrae variables make them excellent probes of the
formation and evolution of a stellar population. The mere presence of such
stars necessitates an age greater than ~10 Gyr while their periods and
amplitudes can be used to estimate the metal abundance of the cluster or galaxy
in which they reside. These and other features of RR Lyraes have been used to
study the properties of M31 and M33. Though these studies are generally in
their infancy, we have established that M31 and M33 do indeed harbor RR Lyraes
in their halos and probably also in their disks suggesting that these two
components formed early in the history of M31 and M33. The mean metallicities
of the halo RR Lyraes in these galaxies are consistent with those of other halo
stellar population tracers such as the dwarf spheroidal satellites of M31 and
the halo globular clusters in M33. Little is known about the spatial
distribution of the RR Lyraes, especially in M33. This will require wide-field
time-series studies with sufficient photometric depth to allow both the
identification of RR Lyraes and robust period determination.

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The categories of this paper are: nucl-th
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The categories of this paper are: hep-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: math
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The categories of this paper are: q-bio
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The categories of this paper are: supr-con
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The categories of this paper are: solv-int
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The categories of this paper are: gr-qc
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The categories of this paper are: nlin
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: alg-geom
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The categories of this paper are: dg-ga
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The categories of this paper are: econ