Another cluster of red supergiants close to RSGC1

¹ Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain e-mail: ignacio.negueruela@ua.es
² Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK

Received: 29 September 2009
Accepted: 5 January 2010

Abstract

Context. Recent studies have revealed massive star clusters in a region of the Milky Way close to the tip of the Long Bar. These clusters are heavily obscured and are characterised by a population of red supergiants.

Aims. We analyse a previously unreported concentration of bright red stars ~16' away from the cluster RSGC1

Methods. We utilised near IR photometry to identify candidate red supergiants and then K-band spectroscopy of a sample to characterise their properties.

Results. We find a compact clump of eight red supergiants and five other candidates at some distance, one of which is spectroscopically confirmed as a red supergiant. These objects must form an open cluster, which we name Alicante 8. Because of the high reddening and strong field contamination, the cluster sequence is not clearly seen in 2MASS or UKIDSS near-IR photometry. From the analysis of the red supergiants, we infer an extinction = 1.9 and an age close to 20 Myr.

Conclusions. Though this cluster is smaller than the three known previously, its properties still suggest a mass in excess of 10 000 . Its discovery corroborates the hypothesis that star formation in this region has happened on a wide scale between ~10 and ~20 Myr ago.