Metallicity and distance of NGC 6362 from its RR Lyrae and SX Phoenicis stars

TL;DR

This study uses new photometry and Fourier analysis of RR Lyrae stars in NGC 6362 to accurately determine its metallicity and distance, revealing detailed stellar population characteristics.

Contribution

It provides updated metallicity and distance estimates for NGC 6362 using Fourier decomposition of RR Lyrae light curves and discusses the cluster's stellar population and variable star properties.

Findings

Metallicity [Fe/H] ≈ -1.08 to -1.06 from RR Lyrae stars

Distance to NGC 6362 ≈ 8 kpc from RR Lyrae stars

Identification of a foreground SX Phe star and peculiarities in variable star V37

Abstract

New time-series VI CCD photometry of the globular cluster NGC 6362 is studied with the aim of estimating the reddening, mean metallicity and distance of the cluster from its population of RR Lyrae stars. The Fourier decomposition of carefully selected single-mode RR Lyrae light curves, and the use of well-established semi-empirical calibrations and revised zero points, lead to the values of [Fe/H]UVES =1:066 +// 0:126 and -1:08 +/- 0:16 and the distance 7:93 +/- 0:32 and 8:02 +/- 0:15 kpc from the RRab and RRc stars respectively. The distribution of RR Lyrae stars in the horizontal branch shows a neat segregation of pulsating modes about the red edge of the first overtone instability strip, which is not necessarily expected in an OoI type cluster like NGC 6362. Four RRab stars are found likely advanced in their evolution towards the AGB. One new foreground SX Phe star, some 4 kpc in front of the cluster and projected onto the field of our images is reported. We comment on the heavy light contamination, by a very close neighbouring star, of the peculiar double-mode V37 variable, recently postulated as a non-typical RRc variable.