Massive open star clusters using the VVV survey

V. Young clusters with an OB stellar population^⋆

¹ Millenium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
e-mail: sebastian.ramirez@uv.cl
² Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Casilla 5030, Valparaíso, Chile
³ Gemini Observatory, Northern Operations Center, 670 North A’ohoku Place, Hilo, HI 96720, USA
⁴ Universidade Federal do Rio Grande do Sul, Departamento de Astronomia CP 15051, RS, 91501-970 Porto Alegre, Brazil

Received: 27 May 2015
Accepted: 1 February 2016

Abstract

Context. The ESO public survey VISTA Variables in the Vía Láctea (VVV) has contributed with deep multi-epoch photometry of the Galactic bulge and the adjacent part of the disk over 526 sq. deg. More than a hundred cluster candidates have been reported thanks to this survey.

Aims. We present the fifth article in a series of papers focused on young and massive clusters discovered in the VVV survey. In this paper, we present the physical characterization of five clusters with a spectroscopically confirmed OB-type stellar population.

Methods. To characterize the clusters, we used near-infrared photometry (J, H, and K_S) from the VVV survey and near-infrared K-band spectroscopy from ISAAC at VLT, following the methodology presented in the previous articles of the series.

Results. All clusters in our sample are very young (ages between 1–20 Myr), and their total mass are between (1.07^+0.40_-0.30)×10² M_⊙ and (4.17^+4.15_-2.08)×10³ M_⊙. We observed a relation between the clusters total mass M_ecl and the mass of their most massive stellar member m_max, for clusters with an age <10 Myr.