FSR 584 – a new globular cluster in the Galaxy?

¹ Universidade Federal do Rio Grande do Sul, Departamento de Astronomia, CP 15051, RS, Porto Alegre 91501-970, Brazil e-mail: [charles;bica]@if.ufrgs.br
² Università di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio 5, 35122 Padova, Italy e-mail: sergio.ortolani@unipd.it
³ Universidade de São Paulo, Departamento de Astronomia, Rua do Matão 1226 São Paulo 05508-900, Brazil e-mail: barbuy@astro.iag.usp.br

Received: 6 June 2007
Accepted: 22 June 2007

Abstract

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 () 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  kpc, and it is located at ≈1 kpc outside the Solar circle. The radial density profile is characterized by a core radius of R_core 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 , which makes it a limiting object in the optical and explains why it has so far been overlooked.