Discovery of a Probable SX Phoenicis Star in M107 (NGC 6171)

Using V images taken in May and June 2012 with the SARA Consortium's 0.9-meter telescope located at Kitt Peak National Observatory, we searched for variable stars in the globular cluster M107 (NGC 6171). The search was accomplished using the ISIS v2.2 image subtraction software. We refined the positions of the previously known variables and confirmed the 21 RR Lyrae variables from Clement's Catalog of Variable Stars in Globular Clusters (Clement et al. 2001). We also discovered a previously unknown variable which is likely an SX Phoenicis star. For this SX Phoenicis star we measured a fundamental pulsation frequency 19.0122/day (P=0.05257 days) and a mean amplitude of 0.046 magnitudes in the V band. This variable had an average V-band magnitude of 17.72, nearly 2 magnitudes dimmer than the horizontal branch of M107, typical of SX Phoenicis stars and blue stragglers lying just beyond the main sequence turn-off in globular clusters.