Searching for Long-Period Variables in Globular Clusters: A Demonstration on NGC 1851 Using PROMPT

Abstract

We demonstrate how a small, robotically controlled telescope can be used to monitor bright, long-period variable stars in dense stellar systems like Galactic globular clusters. Observations of NGC 1851 gathered with the No. 5 PROMPT 0.4 m telescope in BVRI yielded quality color-magnitude diagrams to well below the horizontal branch at V = 16.1 mag. We recovered many of the known RR Lyrae variables, clarified the nature of the three known bright variables in the cluster, detected two new long-period variables, and flagged seven more suspected variables. We describe methods that should yield good results in variable star searches and monitoring using this and other small telescopes.