A Chandra Study of the Rosette Star-Forming Complex. II. Clusters in the Rosette Molecular Cloud

摘要

We explore here the young stellar populations in the Rosette Molecular Cloud(RMC) region with high spatial resolution X-ray images from the Chandra X-rayObservatory, which are effective in locating weak-lined T Tauri stars as wellas disk-bearing young stars. A total of 395 X-ray point sources are detected,299 of which (76%) have an optical or near-infrared (NIR) counterpartidentified from deep FLAMINGOS images. From X-ray and mass sensitivity limits,we infer a total population of about 1700 young stars in the survey region.Based on smoothed stellar surface density maps, we investigate the spatialdistribution of the X-ray sources and define three distinctive structures andsubstructures within them. Structures B and C are associated with previouslyknown embedded IR clusters, while structure A is a new X-ray-identifiedunobscured cluster. A high mass protostar RMCX #89 = IRAS 06306+0437 and itsassociated sparse cluster is studied. The different subregions are not coevalbut do not show a simple spatial-age pattern. Disk fractions vary betweensubregions and are generally 20% of the total stellar population inferred fromthe X-ray survey. The data are consistent with speculations that triggered starformation around the HII region is present in the RMC, but do not support asimple sequential triggering process through the cloud interior. While asignificant fraction of young stars are located in a distributed populationthroughout the RMC region, it is not clear they originated in clusteredenvironments.