A Multiband Photometric Study of RR Lyrae Stars in M53 (NGC 5024)

TL;DR

This study uses extensive multiband photometry over 22 years to analyze RR Lyrae stars in M53, refining their properties and accurately determining the cluster's distance, confirming its Oosterhoff II classification.

Contribution

It provides a comprehensive multiband analysis of RR Lyrae stars in M53, including refined periods, mean magnitudes, and a precise distance measurement using period-luminosity relations.

Findings

Confirmed M53 as an Oosterhoff II cluster with specific period averages.

Derived accurate distance modulus of 16.242 mag, corresponding to 17.717 kpc.

Established period-luminosity and Wesenheit relations consistent with theoretical models.

Abstract

We present a multiband (UBVRI) time-series photometric study of RR Lyrae (RRL) stars in the globular cluster Messier 53 (NGC 5024) to refine their pulsation properties and determine a precise cluster distance. The archival photometric data includes images taken over 22 years and 3 months using different optical telescopes, providing an excellent time baseline to investigate light curves of variable stars. Using Lomb-Scargle periodogram, we derived accurate periods for 29 fundamental-mode (RRab) and 35 first-overtone (RRc) RRLs. Template-fitting to phase-folded light curves provided robust mean magnitudes and amplitudes. The refined periods confirm M53 as an Oosterhoff II cluster, with a mean period of 0.649 days for RRab and 0.346 days for RRc, and a high RRc fraction (54.7\%). Most RRLs align with the horizontal branch in the color-magnitude diagram, while a few outliers result from blending effects. Period-amplitude diagrams show RRab stars following the Oosterhoff II locus. We derived I-band period-luminosity and multi-band period-Wesenheit relations, comparing them with theoretical predictions. A weighted mean distance modulus of 16.242 $\pm$ 0.05 mag yields a cluster distance of 17.717 $\pm$ 0.408 kpc, in agreement with recent estimates based on parallaxes from Gaia data.