A third red supergiant rich cluster in the Scutum-Crux arm

¹ Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK e-mail: S.Clark@open.ac.uk
² Departamento. de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
³ School of Physics & Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
⁴ Chester F. Carlson Centre for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester NY 14623, USA
⁵ Astronomical Institute of St. Petersburg University, Petrodvorets, Universitetsky pr. 28, 198504 St. Petersburg, Russia
⁶ Isaac Newton Institute of Chile, St. Petersburg branch, Russia
⁷ IBM United Kingdom Laboratories, Hursley Park, Winchester, Hampshire SO21 2JN, UK
⁸ Department of Physics & Astronomy, University of Sheffield, Sheffield S3 7RH, UK
⁹ Pulkovo Astronomical Observatory, 196140 St. Petersburg, Russia

Received: 25 February 2009
Accepted: 8 March 2009

Abstract

Aims. We aim to characterise the properties of a third massive, red supergiant dominated galactic cluster.

Methods. To accomplish this we utilised a combination of near/mid- IR photometry and spectroscopy to identify and classify the properties of cluster members, and statistical arguments to determine the mass of the cluster.

Results. We found a total of 16 strong candidates for cluster membership, for which formal classification of a subset yields spectral types from K3–M4 Ia and luminosities between –4.8 for an adopted distance of kpc. For an age in the range of 16–20 Myr, the implied mass is 2–, making it one of the most massive young clusters in the Galaxy. This discovery supports the hypothesis that a significant burst of star formation occurred at the base of Scutum-Crux arm between 10–20 Myr ago, yielding a stellar complex comprising at least ~10⁵  of stars (noting that since the cluster identification criteria rely on the presence of RSGs, we suspect that the true stellar yield will be significantly higher). We highlight the apparent absence of X-ray binaries within the star formation complex and finally, given the physical association of at least two pulsars with this region, discuss the implications of this finding for stellar evolution and the production and properties of neutron stars.