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

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 log(L/L� ) ∼ 4.5–4.8 for an adopted distance of 6 ± 1 kpc. For an age in the range of 16–20 Myr, the implied mass is 2–4×10 4 M� , 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