Astrophys. J., Suppl. Ser., 168, 100-127 (2007/January-0)
An X-ray census of young stars in the massive southern star-forming complex NGC 6357.
WANG J., TOWNSLEY L.K., FEIGELSON E.D., GETMAN K.V., BROOS P.S., GARMIRE G.P. and TSUJIMOTO M.
Abstract (from CDS):
We present the first high spatial resolution X-ray study of the massive star-forming region NGC 6357, obtained in a 38 ks Chandra/ACIS observation. Inside the brightest constituent of this large H II region complex is the massive open cluster Pismis 24. It contains two of the brightest and bluest stars known, yet remains poorly studied; only a handful of optically bright stellar members have been identified. We investigate the cluster extent and initial mass function and detect ∼800 X-ray sources with a limiting sensitivity of ∼1030 ergs/s; this provides the first reliable probe of the rich intermediate-mass and low-mass population of this massive cluster, increasing the number of known members from optical study by a factor of ∼50. The high-luminosity end (logLh[2-8 keV]≥30.3 ergs/s) of the observed X-ray luminosity function in NGC 6357 is clearly consistent with a power-law relation as seen in the Orion Nebula Cluster and Cepheus B, yielding the first estimate of NGC 6357's total cluster population, a few times the known Orion population. We investigate the structure of the cluster, finding small-scale substructures superposed on a spherical cluster with 6 pc extent, and discuss its relationship to the nebular morphology. The long-standing LX-10–7Lbolcorrelation for O stars is confirmed. Twenty-four candidate O stars and one possible new obscured massive YSO or Wolf-Rayet star are presented. Many cluster members are estimated to be intermediate-mass stars from available infrared photometry (assuming an age of ∼1 Myr), but only a few exhibit K-band excess. We report the first detection of X-ray emission from an evaporating gaseous globule at the tip of a molecular pillar; this source is likely a B0-B2 protostar.
ISM: Individual: NGC Number: NGC 6357 - open clusters and associations: individual (Pismis 24) - Stars: Formation - Stars: Luminosity Function, Mass Function - Stars: Pre-Main-Sequence - X-Rays: Stars
VizieR on-line data:
<Available at CDS (J/ApJS/168/100): table1.dat table2.dat table3.dat table4.dat table5.dat table6.dat table8.dat>
Table 1: [WTF2007] NNN (Nos 1-779).
Status at CDS:
could be processed
// All or part of tables of objects could be ingested in SIMBAD with priority 2.
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