Massive open star clusters using the VVV survey^⋆

II. Discovery of six clusters with Wolf-Rayet stars

¹ Departamento de Física y AstronomíaUniversidad de Valparaíso n Av. Gran Bretaña 1111, Playa Ancha, 5030 Casilla, Chile
e-mail: andrenicolas.chene@gmail.com
² Departamento de Astronomía, Universidad de Concepción, Casilla 160, Chile
³ The Milky Way Millennium Nucleus, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
⁴ Universidade Federal do Rio Grande do Sul, Departamento de Astronomia, CP 15051, RS, 91501-970 Porto Alegre, Brazil
⁵ Saint Mary’s University, Halifax, Nova Scotia, Canada
⁶ Facultad de Ciencias Astronómicas y Geofísicas (UNLP), Instituto de Astrofísica de La Plata (CONICET, UNLP), Paseo del Bosque s/n, La Plata, Argentina
⁷ University of Hertfordshire, Hatfield, AL10 9AB, UK
⁸ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁹ Laboratoire d’Astrophysique de Marseille – LAM, Université d’Aix-Marseille, CNRS, UMR 7326, 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
¹⁰ Pontificia Universidad Católica de Chile, Facultad de Física, Departamento de Astronomía y Astrofísica, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
¹¹ School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, UK
¹² Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian District, 100871 Beijing, PR China
¹³ Groupe d’Astrophysique des Hautes Énergies, Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août, Batiment B5c, 4000 Liège, Belgium
¹⁴ European Southern Observatory, Ave. Alonso de Cordova 3107, Casilla 19, Chile
¹⁵ Centro de Astrofisica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁶ LUPM-UMR 5299, CNRS, Université Montpellier II, Place Eugène Bataillon, 34095, Montpellier Cedex 05, France
¹⁷ Vatican Observatory, V 00120 Vatican City State, Italy
¹⁸ Department of Astrophysical Sciences, Princeton University, Princeton NJ 08544-1001, USA

Received: 26 July 2012
Accepted: 8 November 2012

Abstract

Context. The ESO Public Survey “VISTA Variables in the Vía Láctea” (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. Nearly 150 new open clusters and cluster candidates have been discovered in this survey.

Aims. This is the second in a series of papers about young, massive open clusters observed using the VVV survey. We present the first study of six recently discovered clusters. These clusters contain at least one newly discovered Wolf-Rayet (WR) star.

Methods. Following the methodology presented in the first paper of the series, wide-field, deep JHK_s VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters for a subset of clusters.

Results. We find that the six studied stellar groups are real young (2–7 Myr) and massive (between 0.8 and 2.2 × 10³ M_⊙) clusters. They are highly obscured (A_V ~ 5−24 mag) and compact (1–2 pc). In addition to WR stars, two of the six clusters also contain at least one red supergiant star, and one of these two clusters also contains a blue supergiant. We claim the discovery of 8 new WR stars, and 3 stars showing WR-like emission lines which could be classified WR or OIf. Preliminary analysis provides initial masses of  ~30–50 M_⊙ for the WR stars. Finally, we discuss the spiral structure of the Galaxy using the six new clusters as tracers, together with the previously studied VVV clusters.