The Young Stellar Population in M17 Revealed by Chandra

We report here results from a Chandra ACIS observation of the stellarpopulations in and around the Messier 17 H II region. The field reveals 886sources, 771 of which have stellar counterparts in infrared images. In additionto comprehensive tables of X-ray source properties, several results arepresented: * The X-ray Luminosity Function is calibrated to that of the OrionNebula Cluster population to infer a total population of roughly 8000--10,000stars * About 40% of the ACIS sources are heavily obscured with A_V > 10 mag.Some are concentrated around well-studied star-forming regions but most aredistributed across the field. X-ray emission is detected from 64 of thehundreds of Class I protostar candidates that can be identified by near- andmid-infrared colors. These constitute the most likely protostar candidatesknown in M17. * The spatial distribution of X-ray stars is complex: we find anew embedded cluster, a 2 pc-long arc of young stars along the southwest edgeof the M17 H II region, and 0.1 pc substructure within various populations.These structures may indicate that the populations are dynamically young. * All(14/14) of the known O stars but only about half (19/34) of the known B0--B3stars in the M17 field are detected. Six of these stars exhibit very hardthermal plasma components (kT>4 keV) that may be due to colliding windbinaries. More than 100 candidate new OB stars are found, including 28 X-raydetected intermediate- and high-mass protostar candidates with infraredexcesses. * Only a small fraction (perhaps 10%) of X-ray selected high- andintermediate- mass stars exhibit K-band emitting protoplanetary disks,providing further evidence that inner disks evolve very rapidly around moremassive stars.