Variable Stars in Metal-Rich Globular Clusters. III. NGC 6539

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 …