Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Deep 2MASS Photometry of M67 and Calibration of the Main Sequence J-Ks
  Color Difference as an Age Indicator   We present an analysis of Two Micron All Sky Survey (2MASS) calibration
photometry of the old open cluster M67 (NGC 2682). The proper motion-cleaned
color-magnitude diagram (CMD) resulting from these data extends ~3 magnitudes
deeper than one based on data from the point source catalog. The CMD extends
from above the helium-burning red clump to a faint limit that is more than 7
magnitudes below the main sequence turnoff in the Ks band. After adopting a
reddening of E(B-V) = 0.041 +/- 0.004 and a metal abundance of [Fe/H] = -0.009
+/- 0.009 based on a survey of published values, we fit the unevolved main
sequence of M67 to field main sequence stars with 2MASS photometry and
Hipparcos parallaxes. This analysis yields distance moduli of (m-M)Ks = 9.72
+/- 0.05 and (m-M)o = 9.70 +/- 0.05, which are consistent with published
values. We compare the theoretical isochrones of Girardi et al. and Dotter et
al. to the CMD of M67 and comment on the relative merits of each set of models.
These comparisons suggest an age between 3.5 and 4.0 Gyr for M67. The depth of
the M67 data make them ideal for the calibration of a new age indicator that
has recently been devised by Calamida et al.- the difference in (J-Ks) color
between the main sequence turnoff (TO) and the point on the lower main sequence
where it turns down (TD) and becomes nearly vertical [D(J-Ks)]. Coupled with
deep 2MASS photometry for three other open clusters, NGC 2516, M44, and NGC
6791, we calibrate D(J-Ks) in terms of age and find D(J-Ks) = (3.017 +/- 0.347)
- (0.259 +/- 0.037)*Log Age (yrs).

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The categories of this paper are: q-alg
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The categories of this paper are: nucl-th
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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: solv-int
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The categories of this paper are: q-bio
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The categories of this paper are: eess
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The categories of this paper are: atom-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: chem-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: chao-dyn
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The categories of this paper are: cs
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The categories of this paper are: ao-sci
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The categories of this paper are: stat
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The categories of this paper are: supr-con