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 \citep clement01 .
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 \mathrm { day } ^ { -1 } ( 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 .