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X-Ray and IR Point Source Identification and Characteristics in the Embedded, Massive Star-Forming Region RCW 108
We report on the results of an approximately 90 ks Chandra observationof a complex region that hosts multiple sites of recent and active starformation in ARA OB1a. The field is centered on the embedded cluster RCW108-IR and includes a large portion of the open cluster NGC 6193. Wedetect over 420 X-ray sources in the field and combined these data withdeep near-IR, Spitzer/IRAC and Midcourse Space Experiment (MSX) mid-IRdata. We find about 360 of the X-ray sources have near-IR counterparts.We divide the region into five parts based on the X-ray point sourcecharacteristics and extended 8 μm emission. The most clearly definedregions are the central region, identified by embedded sources with highluminosities in the both the near-IR and X-ray as well as high X-raytemperatures (~3 keV), and the eastern region, identified by lowextinction and ~1 keV X-ray temperatures. Other regions, identified bytheir directional relationship to RCW 108-IR, are lessuniform—representing combinations of the first two regions,independent star formation epochs, or both. The cluster members range inX-ray luminosity from 1029 to 1033 ergs-1. Over 18% of the cluster members with over 100 countsexhibit flares. All sources with over 350 counts are variable. Overallabout 10% (16% in RCW 108-IR) appear to have optically thick disks asderived from their position in the (J - H), (H - K) diagram. The diskfraction becomes much higher when IRAC data are employed. The largestfraction of X-ray sources is best described as possessing some diskmaterial via a more detailed extinction fitting. We fit the bulk of theX-ray spectra as absorbed Raymond-Smith-type plasmas, and find that thecolumn to the RCW 108-IR members varies from 1021 to1023 cm-2. We find that the field contains 41candidate O or B stars, and estimate that the total number ofpre-main-sequence stars in the field is about 1600 ± 200.Approximately 800 are confined to the 3' (~1.1 pc) central region.
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