The variable stars in the compact halo globular cluster NGC 5634 visited again

TL;DR

This study provides detailed photometry and membership analysis of RR Lyrae stars in NGC 5634, deriving its metallicity and distance using Fourier decomposition, and clarifies the variability status of certain stars.

Contribution

It offers new time-series photometry, accurate variable star parameters, and independent metallicity and distance estimates for NGC 5634 using Gaia data and Fourier analysis.

Findings

Confirmed variability of RRab star V7.

Derived metallicity [Fe/H] ≈ -1.68 for the cluster.

Estimated distance to NGC 5634 as approximately 23 kpc.

Abstract

We present new time-series CCD \emph{VR} photometry of the globular cluster NGC 5634. We aim to use the known RR Lyrae stars, members of the cluster, as indicators of mean metallicity and distance. Accurate coordinates, periods and an identification chart of the variables in the field of our images are provided. A membership analysis was performed, based on $Gaia$-DR3 proper motions, for 3525 point sources within 15 arcmin from the cluster center. The membership status for each known variable was established and it was found that V10, V11 and V16 are most likely field stars. The variability of the RRab star V7, considered non-variable for a number of years, is demonstrated. Via the Fourier decomposition of the light curves of cluster member RR Lyrae, the mean metallicity and distance were calculated independently from RRab and RRc stars to find [Fe/H]$_{\rm ZW}= -1.67 \pm 0.11$ y $D=23.9 \pm 0.8$ kpc, and [Fe/H]$_{\rm ZW}= -1.69 \pm 0.22$ y $D=22.9 \pm 1.0$ kpc respectively.