Three Galactic globular cluster candidates^⋆

¹ Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile
e-mail: cmbidin@astro-udec.cl
² Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago, Chile
³ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
⁴ European Southern Observatory, Avda Alonso de Cordova, 3107, Casilla 19001, Santiago, Chile
⁵ Departamento de Física, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, RN, Brazil
⁶ Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
⁷ Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK

Received: 16 June 2011
Accepted: 30 August 2011

Abstract

Context. The census of Galactic globular clusters (GCs) is still incomplete, and about ten new objects are supposed to await discovery, hidden behind the crowded and reddened regions of the Galactic bulge and disk.

Aims. We investigated the nature of three new GC candidates, discovered in the frames collected by the Vista Variables in the Via Lactea (VVV) near-infrared survey. They will be called VVV CL002, VVV CL003, and VVV CL004.

Methods. We studied the results of point-spread-function near-infrared photometry from VVV data for the three objects and their surrounding fields, the proper motion information available in the literature and, when possible, we derived the cluster parameters by means of calibrated indices measured on the color–magnitude diagrams.

Results. The evidence shows that VVV CL002 is a newly discovered, small, moderately metal-rich ( [Fe/H]  ≈  − 0.4) Galactic GC. It is located at a Galactocentric distance of 0.7  ±  0.9 kpc, and it could be one of the nearest GC to the Galactic center. Its characteristics are more similar to those of low-mass, Palomar-like GCs than to more classical, old, and massive bulge GCs. VVV CL003 is the first star cluster discovered in the Galactic disk on the opposite side of the center with respect to the Sun, at a Galactocentric distance of  ~5 kpc. Its high metallicity ( [Fe/H]  ≈  − 0.1) and location point to an open cluster, but a GC cannot be excluded. VVV CL004, on the contrary, is most probably only a random clump of field stars, as indicated by both its low statistical significance and by the impossibility to distinguish its stars from the surrounding field population.

Conclusions. We claim the detection of i) a new Galactic GC, deriving an estimate of its basic parameters; ii) a stellar aggregate, probably an open cluster, in the disk directly beyond the Galactic center; and iii) an overdensity of stars, most probably an asterism.