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Arxiv: EWOCS-III: JWST observations of the supermassive star cluster Westerlund 1 Published: 11/20/2024 7:52:21 AM Updated: 11/20/2024 7:52:21 AM

Paper abstract: The typically large distances, extinction, and crowding of Galacticsupermassive star clusters have so far hampered the identification of theirvery low mass members, required to extend our understanding of star and planetformation, and early stellar evolution, to starburst. This situation has nowevolved thanks to the James Webb Space Telescope (JWST), and its unmatchedresolution and sensitivity in the infrared. In this paper, the third of theseries of the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS), wepresent JWST/NIRCam and JWST/MIRI observations of the supermassive star clusterWesterlund 1. These observations are specifically designed to unveil thecluster members down to the BD mass regime, and to allow us to select and studythe protoplanetary disks and to study the mutual feedback between the clustermembers and the surrounding environment. Westerlund 1 was observed as part ofJWST GO-1905 for 23.6 hours. The data have been reduced using the JWSTcalibration pipeline, together with specific tools necessary to removeartifacts. Source identification and photometry were performed with DOLPHOT.The MIRI images show a plethora of different features. Diffuse nebular emissionis observed around the cluster, which is typically composed of myriads ofdroplet-like features pointing toward the cluster center or the group ofmassive stars surrounding the WR star W72/A. A long pillar is also observed inthe NW. The MIRI images also show resolved shells and outflows surrounding theM-type RSG W20, W26, W75, and W237, the sgB[e] star W9 and the YHG W4. Thecolor-magnitude diagrams built using the NIRCam photometry show a clear clustersequence, which is marked in its upper part by the 1828 NIRCam stars with X-raycounterparts. NIRCam observations using the F115W filter have reached the 23.8mag limit with 50\% completeness (roughly corresponding to a 0.06 Msol browndwarf).