FSR1767 - a new globular cluster in the Galaxy

TL;DR

This paper confirms FSR 1767 as the closest globular cluster in the Galaxy, detailing its properties, structure, and motion, and highlighting its previous oversight due to moderate absorption and contamination.

Contribution

It provides the first detailed characterization of FSR 1767 as an intermediate metallicity globular cluster using multi-method analysis.

Findings

FSR 1767 is the closest globular cluster at 1.5 kpc from the Sun.

It has properties consistent with a Palomar-like globular cluster.

The cluster's core and tidal radii are 0.24 and 3.1 pc, respectively.

Abstract

The globular cluster (GC) nature of the recently catalogued candidate FSR 1767 is established in the present work. It results as the closest GC so far detected in the Galaxy. The nature of this object is investigated by means of 2MASS colour-magnitude diagrams (CMDs), the stellar radial density profile (RDP) and proper-motions (PM). The properties are consistent with an intermediate metallicity ($\feh\approx-1.2$) GC with a well-defined turnoff (TO), red-giant branch (RGB) and blue horizontal-branch (HB). The distance of FSR 1767 from the Sun is $\ds\approx1.5$ kpc, and it is located at the Galactocentric distance $\rgc\approx5.7$ kpc. With the space velocity components $(V,W)=(184\pm14,-43\pm14)\rm km s^{-1}$, FSR 1767 appears to be a Palomar-like GC with $\mv\approx-4.7$, that currently lies $\approx57$ pc below the Galactic plane. The RDP is well represented by a King profile with the core and tidal radii $\rc=0.24\pm0.08$ pc and $\rt=3.1\pm1.0$ pc, respectively, with a small half-light radius $\rh=0.60\pm0.15$ pc. The optical absorption is moderate for an infrared GC, $A_V=6.2\pm0.3$, which together with its central direction and enhanced contamination explains why it has so far been overlooked.