Massive stars in the young cluster VVV CL074

F Martins,A.-N Chené,J.-C Bouret,J Borissova,J Groh,D Minniti,S Ramírez Alegría

doi:10.1051/0004-6361/201935605

Abstract

Context. The evolution of massive stars is not fully constrained. Studies of young massive clusters hosting various populations of massive stars can help refine our understanding of the life and fate of massive stars. Aims. In this context, our goal is to study the massive stellar content of the young massive cluster VVV CL074. Methods. We obtained K-band spectroscopy of the brightest cluster members in order to identify the massive star population. We also determined the stellar properties of the cluster’s massive stars to better quantify the evolutionary sequences linking different types of massive stars. We collected integral field spectroscopy of selected fields in the cluster VVV CL074 with SINFONI on the ESO/VLT. We performed a spectral classification based on the K-band spectra and comparison to infrared spectral atlases. We determined the stellar parameters of the massive stars from analysis with atmosphere models computed with the code CMFGEN. Results. We uncover a population of 25 early-type (OB and Wolf–Rayet) stars, 19 being newly discovered by our observations out of which 15 are likely cluster members. The cluster’s spectrophotometric distance is 10.2 ± 1.6 kpc, placing it close to the intersection of the galactic bar and the Norma arm, beyond the galactic center. This makes VVV CL074 one the farthest young massive clusters identified so far. Among the massive stars population, three objects are Wolf–Rayet stars, the remaining are O and B stars. From the Hertzsprung–Russell diagram we find that most stars have an age between 3 and 6 Myr according to the Geneva evolutionary tracks. WN8 and WC8-9 stars are the descendants of stars with initial masses between 40 and 60 M⊙. The massive star population of VVV CL074 is very similar to that of the cluster DBS2003-179 and to a lesser extent to that of the Quintuplet cluster, indicating the same age. The central cluster of the Galaxy is ∼3 Myr older. From the comparison of the massive stars populations in these four clusters, one concludes that galactic stars with an initial mass in the range 40–60 M⊙ likely go through a WN8-9 phase.

Highlights

Massive stars are born as O and B stars and live as such while they stay on the main sequence
Stars showing CO absorption band-heads, if they belong to the VISTA Variables in the Vía Láctea (VVV) CL074 cluster, can be red supergiants (RSG) or asymptotic giant branch (AGB) stars depending on their initial mass
Most of the OB stars are located between the 3 and 6 Myr isochrones. They are located on the main sequence and have initial masses between ∼20 and ∼60 M

Summary

Introduction

Massive stars are born as O and B stars and live as such while they stay on the main sequence. Another approach is to study several samples of massive stars, each with a given age This way we get snapshots of stellar evolution at different times and, post-main sequence evolution being much faster than hydrogen-burning, the progenitors and evolution of evolved massive stars can be better identified. This approach can be conducted by studying young massive clusters (Martins et al 2007, 2008; Davies et al 2007, 2008, 2012a,b; Negueruela et al 2010; Liermann et al 2012; Borissova et al 2012; Ramírez Alegría et al 2012, 2014b). We compare VVV CL074 with other prototypical young massive galactic clusters

Observations and data reduction

Stellar content and spectral types

Stellar parameters

CO absorption stars

Evolutionary status

Comparison to other clusters