lovely image showing the cluster, and some of the associated OB association, and part of the giant arc of nebulosity on one side of the cluster.
I seem to recall that the cluster is one of the most prominent groups of (supergiant & superluminous) OB stars in local space.
I can't remember whether the supergiant arc of nebulosity is caused by the energy emitted from the cluster stars or by a supernova.
Here is a larger section of the supergiant arc or shell, from wikisky:
