Obscured clusters. II. GLIMPSE-C02 - A new metal rich globular cluster in the Milky Way

TL;DR

This paper reports the discovery and detailed analysis of GLIMPSE-C02, a new metal-rich globular cluster in the Milky Way, identified through infrared observations and spectroscopy, expanding knowledge of the Galaxy's hidden stellar populations.

Contribution

The study presents the first detailed characterization of GLIMPSE-C02, including its metallicity, distance, and structural parameters, demonstrating it as a previously unknown, metal-rich globular cluster in the Milky Way.

Findings

GLIMPSE-C02 is a new, metal-rich globular cluster in the Milky Way.

The cluster is located at the inner edge of the thin disk and transition region with the bulge.

It has a core radius of 0.9 pc and a tidal radius of 20 pc.

Abstract

The estimated total number of Milky Way globulars is 160+-20. The question of whether there are any more undiscovered globular clusters in the Milky Way is particularly relevant with advances in near and mid-IR instrumentation. This investigation is a part of a long-term project to search the inner Milky Way for hidden star clusters and to study them in detail. GLIMPSE-C02 (G02) is one of these objects, situated near the Galactic plane (l=14.129deg, b=-0.644deg). Our analysis is based on SOFI/NTT JHKs imaging and low resolution (R~1400) spectroscopy of three bright cluster red giants in the K atmospheric window. We derived the metal abundance by analysis of these spectra and from the slope of the RGB. The cluster is deeply embedded in dust and undergoes a mean reddening of Av~24.8+-3 mag. The distance to the object is D=4.6+-0.7kpc. The metal abundance of G02 is [Fe/H](H96)=-0.33+-0.14 and [Fe/H](CG)=-0.16+-0.12 using different scales. The best fit to the radial surface brightness profile with a single-mass King's model yields a core radius rc=0.70 arcmin (0.9pc), tidal radius rt=15 arcmin (20pc), and central oncentration c=1.33. We demonstrate that G02 is new Milky Way globular cluster, among the most metal rich globular clusters in the Galaxy. The object is physically located at the inner edge of the thin disk and the transition region with the bulge, and also falls in the zone of the "missing" globulars toward the central region of the Milky Way.