A new search for variable stars in the globular cluster NGC 6366

TL;DR

This study reports the discovery of various variable stars in NGC 6366 using CCD photometry, estimates the cluster's distance and metallicity, and discusses the membership status of a key RR Lyrae star.

Contribution

It introduces new variable star discoveries in NGC 6366 and provides refined estimates of the cluster's properties using Fourier analysis and period-luminosity relationships.

Findings

Discovered multiple types of variable stars including Anomalous Cepheids and SX Phe.

Estimated the cluster's distance at approximately 2.7-3.2 kpc.

Provided metallicity estimate of [Fe/H] = -0.87 for the RRab star.

Abstract

New CCD photometry of NGC 6366 has lead to the discovery of some variable stars. Two possible Anomalous Cepheids (or Pop II Cepheids), three long period variables, one SX Phe and one eclipsing binary have been found. Also a list of 10 candidate variables is reported. The light curve of the RRab star, V1, has been decomposed into its Fourier harmonics, and the Fourier parameters were used to estimate the star's metallicity and distance; [Fe/H] = -0.87 +- 0.14 and d = 3.2 +- 0.1 kpc. It is argued that V1 may not be a member of the cluster but rather a more distant object. If this is so, an upper limit for the distance to the cluster of 2.8 +- 0.1 kpc can be estimated. The P-L relationship for SX Phe stars and the identified modes in the newly discovered SX Phe variable, V6, allow yet another independent determination of the distance to the cluster of d = 2.7 \+- 0.1 kpc. The M_V - {\rm [Fe/H]} relationship for RR Lyrae stars is addressed and the case of V1 is discussed.