Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Variable stars in the field of open cluster NGC 6939   The results of CCD photometric survey performed with the 90/180 cm
Schmidt-Cassegrain Telescope of the Nicolaus Copernicus University Astronomical
Observatory in Piwnice (Poland) and the 70/172 cm Schmidt Telescope of the
National Astronomical Observatory (NAO) at Rozhen (Bulgaria) of the field of 1
Gyr old open cluster NGC 6939 are presented. Twenty two variable stars were
detected, four of them previously known. Four eclipsing systems (3 detached and
1 contact binary) were found to be members of the cluster. Analysis of the
brightness of the contact binary V20 strongly supports the distance to the
cluster of 1.74 +/- 0.20 kpc. The small population of contact binaries in NGC
6939 confirms also the relatively young age of the cluster.

1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
7
The categories of this paper are: hep-th
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
2
The categories of this paper are: math
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg