Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evidence for Extended Star Formation in the Old, Metal-Rich Open
  Cluster, NGC 6791?   NGC 6791 is an old, metal-rich star cluster normally considered to be a disk
open cluster. Its red giant branch is broad in color yet, to date, there is no
evidence for a metallicity spread among its stars. The turnoff region of the
main sequence is also wider than expected from broad-band photometric errors.
Analysis of the color-magnitude diagram reveals a color gradient between the
core of the cluster and its periphery; we evaluate the potential explanations
for this trend. While binarity and photometric errors appear unlikely,
reddening variations across the face of the cluster cannot be excluded. We
argue that a viable alternative explanation for this color trend is an age
spread resulting from a protracted formation time for the cluster; the stars of
the inner region of NGC 6791 appear to be older by ~1 Gyr on average than those
of the outer region.

10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th
8
The categories of this paper are: hep-ex
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an