Investigation of the M13 Globular Cluster: Characteristics and Pulsation Periods of Its RR Lyrae Stars V8, V31, and V54

Volume 52 number 1 (2024)

Daniel Vurgaftman: Stanford Online High School, 415 Broadway Academy Hall, Floor 2, 8853, Redwood City, CA 94063; danyavur@gmail.com, kalee7798@gmail.com. There are two corresponding authors in this study; contributions of the first two authors were equal.
Katherine Lee: Stanford Online High School, 415 Broadway Academy Hall, Floor 2, 8853, Redwood City, CA 94063; danyavur@gmail.com, kalee7798@gmail.com. There are two corresponding authors in this study; contributions of the first two authors were equal.
Jett Peters: Stanford Online High School, 415 Broadway Academy Hall, Floor 2, 8853, Redwood City, CA 94063; jettpeters2@gmail.com
Justin Wang: Stanford Online High School, 415 Broadway Academy Hall, Floor 2, 8853, Redwood City, CA 94063; justinw16688@gmail.com
Kalée Tock: Stanford Online High School, 415 Broadway Academy Hall, Floor 2, 8853, Redwood City, CA 94063; kaleeg@stanford.edu

Abstract

Images of the Messier 13 (M13/NGC 6205) globular cluster were requested from the Las Cumbres Global Observatory’s 40-centimeter telescope to investigate the chemical composition and characteristics of the cluster along with three of its RR Lyrae variable stars. Gaia Data Release 3 data were used to fit an isochrone by varying parameters such as distance, reddening, metallicity, and age. The estimates obtained for these parameters were within uncertainty of the corresponding literature values despite a large range of metallicities that gave an appropriate fit; however, a significantly different proper motion in Right Ascension was used to screen for cluster membership. In addition, the periods for three of the RR Lyrae stars—V8, V31, V54—were confirmed using phase dispersion minimization (string length and standard deviation methods) as well as the Lomb-Scargle method. The colors of three RR Lyrae stars were also investigated through color analysis using data in the Johnson-Cousins V and Sloan Digital Sky Survey I-prime filters. ASAS-SN Sky Patrol data were used to determine if two select stars, V8 and V31, were undergoing period evolution. Because of inconclusive data, further investigation is suggested. Finally, the period-luminosity-metallicity (PLM) relationship was applied to recompute the distance to the cluster. The average derived PLM distance of 7.1 kpcs was a close match to previous distance estimates from the literature.