FSR 584 : a new globular cluster in the galaxy?

Aims. We investigate the nature of the recently catalogued star cluster candidate FSR 584, which is projected in the direction of the molecular cloud W 3 and may be the nearest globular cluster to the Sun. Methods. 2MASS colour-magnitude diagrams, the stellar radial density profile, and proper motions are employed to derive fundamental and structural parameters. Results. The colour-magnitude diagram morphology and the radial density profile show that FSR 584 is an old star cluster. With proper motions, the properties of FSR 584 are consistent with a metal-poor ([Fe/H] ≈ −2) globular cluster with a well-defined turnoff and evidence of a blue horizontal-branch. FSR 584 might be a Palomar-like halo globular cluster that is moving towards the Galactic plane, currently at ≈20 pc above it. The distance from the Sun is dʘ ≈ 1.4 kpc, and it is located at ≈1 kpc outside the Solar circle. The radial density profile is characterized by a core radius of Rcore = 0.3 ± 0.1 pc. However, we cannot exclude the possibility of an old open cluster. Conclusions. Near-infrared photometry coupled to proper motions support the scenario where FSR 584 is a new globular cluster in the Galaxy. The absorption is AV = 9.2 ± 0.6, which makes it a limiting object in the optical and explains why it has so far been overlooked