The main sequence of three red supergiant clusters

Here, we utilize publicly available data from the UKIDSS Galactic Plane Survey. We show that point spread function photometry in conjunction with standard photometric decontamination techniques allows us to identify the most likely MS members in the 10-20 Myr old clusters RSGC 1-3. We confirm the previous detection of the MS in RSGC 2 and provide the first MS detection in RSGC 1 and RSGC 3. There are in excess of 100 stars with more than 8 M-circle dot identified in each cluster. These MS members are concentrated towards the spectroscopically confirmed RSG stars. We utilize the J - K colours of the bright MS stars to determine the K-band extinction towards the clusters. The differential reddening is three times as large in the youngest cluster RSGC 1 as compared to the two older clusters RSGC 2 and RSGC 3. Spectroscopic follow-up of the cluster MS stars should lead to more precise distance and age estimates for these clusters as well as the determination of the stellar mass function in these high-mass environments.