2009A&A...498..109C

We aim to characterise the properties of a third massive, red supergiant dominated galactic cluster. 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. We found a total of 16 strong candidates for cluster membership, for which formal classification of a subset yields spectral types from K3-M4Ia and luminosities between log(L/L_☉)∼4.5-4.8 for an adopted distance of 6±1kpc. For an age in the range of 16-20Myr, the implied mass is 2-4x10⁴M_☉, 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 10-20Myr ago, yielding a stellar complex comprising at least ∼10⁵M_☉ 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.