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

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 semiempirical calibrations and revised zero points, lead to the values of [Fe/H]UVES −1.066 ± 0.126 and −1.08 ± 0.16 and distances of 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 to be likely advanced in their evolution toward 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.