Massive open star clusters using the VVV survey V. Young clusters with an OB stellar population

TL;DR

This study characterizes five young, massive star clusters with OB stellar populations discovered in the VVV survey, providing insights into their physical properties, ages, masses, and a relation between cluster mass and stellar mass.

Contribution

It presents the physical characterization of five young clusters with OB stars using near-infrared photometry and spectroscopy, revealing a mass relation even in very young clusters.

Findings

Clusters are very young (1-20 Myr).

Total masses range from 100 to 4000 solar masses.

A relation exists between cluster mass and the most massive star.

Abstract

The ESO public survey VISTA Variables in the V\'ia L\'actea (VVV) has contributed with deep multi-epoch photometry of the Galactic bulge and the adjacent part of the disk over 526 square degrees. More than a hundred cluster candidates have been reported thanks to this survey. 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. 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. All clusters in our sample are very young (ages between 1-20 Myr), and their total mass are between $(1.07^{+0.40}_{-0.30})\cdot10^2$ $M_{\odot}$ and $(4.17^{+4.15}_{-2.08})\cdot10^3$ $M_{\odot}$. We observed a relation between the clusters total mass $M_{ecl}$ and the mass of their most massive stellar member $m_{max}$, even for clusters with an age $<$ 10 Myr.