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We present Chandra X-ray images of the NGC 2237 young star cluster on theperiphery of the Rosette Nebula. We detect 168 X-ray sources, 80% of which havecounterparts in USNO, 2MASS, and deep FLAMINGOS images. These constitute thefirst census of the cluster members with 0.2<~M<~2 Msun. Star locations innear-infrared color-magnitude diagrams indicate a cluster age around 2 Myr witha visual extinction of 1<Av<3 at 1.4 kpc, the distance of the Rosette Nebula'smain cluster NGC 2244. We derive the K-band luminosity function and the X-rayluminosity function of the cluster, which indicate a population ~400-600 stars.The X-ray-selected sample shows a K-excess disk frequency of 13%. The youngClass II counterparts are aligned in an arc ~3 pc long suggestive of atriggered formation process induced by the O stars in NGC 2244. The disklessClass III sources are more dispersed. Several X-ray emitting stars are locatedinside the molecular cloud and around gaseous pillars projecting from thecloud. These stars, together with a previously unreported optical outfloworiginating inside the cloud, indicate that star formation is continuing at alow level and the cluster is still growing. This X-ray view of young stars onthe western side of the Rosette Nebula complements our earlier studies of thecentral cluster NGC 2244 and the embedded clusters on the eastern side of theNebula. The large scale distribution of the clusters and molecular material isconsistent with a scenario in which the rich central NGC 2244 cluster formedfirst, and its expanding HII region triggered the formation of thenow-unobscured clusters RMC XA and NGC 2237. A large swept-up shell materialaround the HII region is now in a second phase of collect-and-collapsefragmentation, leading to the recent formation of subclusters. Other clustersdeeper in the molecular cloud appear unaffected by the Nebula expansion.

A Chandra Study of the Rosette Star-Forming Complex. III. The NGC 2237 Cluster and the Region's Star Formation History