CCD time-series photometry of the globular cluster NGC 5053: RR Lyrae, Blue Stragglers and SX Phoenicis stars revisited

TL;DR

This study provides detailed CCD time-series photometry of NGC 5053, revising periods of RR Lyrae and SX Phe stars, estimating their physical parameters, and refining the cluster's age, distance, and composition.

Contribution

It offers new period measurements, physical parameter estimates, and a revised classification of Blue Stragglers and variable stars in NGC 5053, enhancing understanding of the cluster's properties.

Findings

RR Lyrae stars have a mean [Fe/H] of -1.97 ± 0.16.

Distance modulus of 16.12 ± 0.04 corresponds to 16.7 ± 0.3 kpc.

Age of the cluster is estimated at 12.5 ± 2.0 Gyr.

Abstract

We report the results of CCD $V$, $r$ and $I$ time-series photometry of the globular cluster NGC 5053. New times of maximum light are given for the eight known RR Lyrae stars in the field of our images and their periods are revised. Their $V$ light curves were Fourier decomposed to estimate their physical parameters. A discussion on the accuracy of the Fourier-based iron abundances, temperatures, masses and radii is given. New periods are found for the 5 known SX Phe stars and a critical discussion of their secular period changes is offered. The mean iron abundance for the RR Lyrae stars is found to be [Fe/H] $\sim -1.97 \pm 0.16$ and lower values are not supported by the present analysis. The absolute magnitude calibrations of the RR Lyrae stars yield an average true distance modulus of $16.12 \pm 0.04$ or a distance of $16.7 \pm 0.3$ kpc. Comparison of the observational CMD with theoretical isochrones indicates an age of $12.5 \pm 2.0$ Gyrs for the cluster. A careful identification of all reported Blue Stragglers (BS) and their $V,I$ magnitudes leads to the conclusion that BS12, BS22, BS23 and BS24 are not BS. On the other hand, three new BS are reported. Variability was found in seven BS, very likely of the SX Phe type in five of them, and in one red giant star. The new SX Phe stars follow established $PL$ relationships and indicate a distance in agreement with the distance from the RR Lyrae stars.