Discovery of a young and massive stellar cluster

Spectrophotometric near-infrared study of Masgomas-1

¹ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
e-mail: sramirez@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
³ Centro de Estudios de Física del Cosmos de Aragón (CEFCA), 44001 Teruel, Spain
e-mail: amarin@cefca.es
⁴ Departamento de Astrofísica, Universidad Complutense de Madrid, 38040 Madrid, Spain

Received: 14 October 2011
Accepted: 13 March 2012

Abstract

Context. Recent near-infrared data have contributed to the discovery of new (obscured) massive stellar clusters and massive stellar populations in previously known clusters in our Galaxy. These discoveries lead us to view the Milky Way as an active star-forming machine.

Aims. The main purpose of this work is to determine physically the main parameters (distance, size, total mass and age) of Masgomas-1, the first massive cluster discovered by our systematic search programme.

Methods. Using near-infrared (J, H, and K_S) photometry we selected 23 OB-type and five red supergiant candidates for multi-object H- and K-spectroscopy and spectral classification.

Results. Of the 28 spectroscopically observed stars, 17 were classified as OB-type, four as supergiants, one as an A-type dwarf star, and six as late-type giant stars. The presence of a supergiant population implies a massive nature of Masgomas-1, supported by our estimate of the cluster initial total mass of (1.94 ± 0.28)  ×  10⁴   M_⊙, obtained after integrating the cluster mass function. The distance estimate of 3.53^+1.55_-1.40 kpc locates the cluster closer than the Scutum-Centaurus base but still within that Galactic arm. The presence of an O9 V star and red supergiants in the same population indicates that the cluster age is in the range of 8 to 10 Myr.