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Title:
Variable Stars in Metal-Rich Globular Clusters. III. NGC 6539
Authors:
Baker, JoDee M.; Layden, Andrew C.; Welch, Douglas L.; Webb, Tracy M. A.
Affiliation:
AA(Department of Physics and Astronomy, Bowling Green State University, Bowling Green, OH, USA; ; Current address: Department of Science, Macomb Community College, Clinton Township, MI, USA.), AB(Department of Physics and Astronomy, Bowling Green State University, Bowling Green, OH, USA; ), AC(Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada), AD(Physics Department, McGill University, Montreal, QC, Canada)
Publication:
The Astronomical Journal, Volume 133, Issue 1, pp. 139-146. (AJ Homepage)
Publication Date:
01/2007
Origin:
UCP
AJ Keywords:
Galaxy: Globular Clusters: Individual: NGC Number: NGC 6539, Stars: Hertzsprung-Russell Diagram, Stars: Horizontal-Branch, Stars: Variables: Other
DOI:
10.1086/509638
Bibliographic Code:
2007AJ....133..139B

Abstract

We present the first CCD-based search for variable stars in the metal-rich globular cluster NGC 6539 ([Fe/H]~-0.7). Our VI photometry of stars within 7' of the cluster center shows a color-magnitude diagram with a normal red clump horizontal-branch morphology without the extension of blue stars seen in two globular clusters of comparable metallicity, NGC 6388 and NGC 6441. We have discovered 13 variable stars, 12 of which are long-period variables (LPVs), and have used infrared photometry from the Two Micron All Sky Survey to further clarify their position in the color-magnitude diagram. We find the specific frequency of these stars, SLPV=0.32, to be comparable to those found in other clusters recently surveyed. We have also detected one RR Lyrae variable star in our data, although it is unlikely to be a cluster member. The color of this star, when compared with low-reddening RR Lyrae stars near the Sun, indicates an interstellar reddening of E(V-I)=1.22 mag toward NGC 6539, in excellent agreement with estimates from the literature.

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