Long-period Variable Stars In The Globular Cluster NGC 6553

Globular clusters (GCs) are home to some of the oldest stellar populations. Many of the stars in GCs are near the end of their life and pulsate due to internal mechanisms that are not fully understood. These long-period variable stars (LPVs) vary in magnitude and radius and have periods of months up to hundreds of days. NGC 6553 is a metal-rich globular cluster located in the crowded bulge of the Milky Way. It has been studied extensively due to its location and metal abundance, but the search for variable stars has been limited to short-period surveys. While 11 LPVs have been documented within NGC 6553, only one has a published period. The dataset consists of images taken in V and I passbands from the Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT) at Cerro Tololo Inter-American Observatory in Chile. Over four years, images were collected on NGC 6553 a few nights a month by previous BGSU students. Photometry was performed on each image using DAOPHOT to track changes in magnitude. The goal of this research was to classify and establish periods for the known LPVs as well as identifying undocumented variable star candidates. Additionally, color magnitude diagrams for the cluster sequence and field population were plotted using the best night of images.