Chandra Study of the Cepheus B Star‐forming Region: Stellar Populations and the Initial Mass Function

Cepheus B (Cep B) molecular cloud and a portion of the nearby Cep OB3b OBassociation, one of the most active regions of star formation within 1 kpc, hasbeen observed with the ACIS detector on board the Chandra X-ray Observatory. Wedetect 431 X-ray sources, of which 89% are confidently identified as clusteredpre-main sequence stars. Two main results are obtained. First, we provide thebest census to date for the stellar population of the region. We identify manymembers of two rich stellar clusters: the lightly obscured Cep OB3bassociation, and the deeply embedded cluster in Cep B whose existence waspreviously traced only by a handful of radio sources and T Tauri stars. Second,we find a discrepancy between the X-ray Luminosity Functions of the Cep OB3band the Orion Nebula Cluster. This may be due to different Initial MassFunctions of two regions (excess of ~0.3 solar mass stars), or different agedistributions. Several other results are obtained. A diffuse X-ray componentseen in the field is attributed to the integrated emission of unresolved lowmass PMS stars. The X-ray emission from HD 217086 (O7n), the principle ionizingsource of the region, follows the standard model involving many small shocks inan unmagnetized radiatively accelerated wind. The X-ray source #294 joins anumber of similar superflare PMS stars where long magnetic structures mayconnect the protoplanetary disk to the stellar surface.Comment: 72 pages, 31 figures, 8 tables. Accepted for publication in Ap