Photometry of the Globular Cluster NGC 3201 and Its Variable Stars

Abstract

We present time series BVI photometry of the brighter stars in the halo globular cluster NGC 3201. We derive high-quality light curves for 58 RR Lyrae stars, all of which appear to be members of the cluster. We determine the foreground reddening of each RR Lyrae star from the star's color and confirm that the reddening varies significantly across the face of the cluster. We obtain a mean value of E(B-V) = 0.25 ± 0.02 mag for stars within 20 of the cluster center. Using the reddening values of the individual RR Lyrae stars, we made dereddened color-magnitude diagrams that reach from the red giant branch tip to ~2 mag below the main-sequence turnoff. Analysis of these diagrams indicates that NGC 3201 has an age of 13–14 Gyr, typical of other globular clusters of its metallicity. We detect low-level brightness variations in most of the cluster's brighter red giant stars and tentatively associate this variation with the small-amplitude red variables seen in the field. We also discovered several δ Scuti variable candidates, two of which appear to be cluster members. The distances derived from the δ Scuti and RR Lyrae stars are in good agreement, indicating d = 4.7 ± 0.2 kpc.