The Metal-Rich Globular Cluster NGC 6366

A photometric investigation of NGC 6366 has yielded a colour–magnitude diagram indicative of a metal-rich globular cluster. The metallicity is estimated from the Hartwick S parameter to be $$[\text{m}/\text{H}]\,=\,-\,0\cdot5\,\pm \,0\cdot2$$. A reddening of $$E(B-V)\,=0\cdot72\pm\,0\cdot02$$ is deduced which yields a corrected distance modulus of $$(m-M)0\,=\,12\cdot 6\pm\,0\cdot2$$. It is suggested that the variable near the cluster centre is an a-type RR Lyrae. If its nature and cluster membership can be confirmed then NGC 6366 provides another opportunity to determine the absolute magnitude of a metal-rich RR Lyrae star.