2007/12/18 by Scott J. Wolk, B. Spitzbart, Bradley D. Spitzbart +6
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Cluster (spacecraft) #Extinction (optical mineralogy) #Galaxy #Luminosity #Optics #Physics #Point source #Star cluster #Stars #Stellar, planetary, and galactic studies #X-ray #astro-ph
paper · pdf · doi:10.1088/0004-6256/135/2/693
63 pages including 18 figures, and 15 tables. Tables 1,2,5,7,10,and 11 have been stubbed in the text and included as ancillary files. Accepted by the Astronomical Journal
arxiv created 2007/12/18 · openalex publication_date 2008/01/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
ABSTRACT We report on the results of an approximately 90 ks Chandra observation of a complex region that hosts multiple sites of recent and active star formation in ARA OB1a. The field is centered on the embedded cluster RCW 108–IR and includes a large portion of the open cluster NGC 6193. We detect over 420 X-ray sources in the field and combined these data with deep near-IR, Spitzer /IRAC and Midcourse Space Experiment ( MSX ) mid-IR data. 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 source characteristics and extended 8 μm emission. The most clearly defined regions are the central region, identified by embedded sources with high luminosities in the both the near-IR and X-ray as well as high X-ray temperatures (∼3 keV), and the eastern region, identified by low extinction and ∼1 keV X-ray temperatures. Other regions, identified by their directional relationship to RCW 108–IR, are less uniform—representing combinations of the first two regions, independent star formation epochs, or both. The cluster members range in X-ray luminosity from 10 29 to 10 33 erg s −1 . Over 18% of the cluster members with over 100 counts exhibit flares. All sources with over 350 counts are variable. Overall about 10% (16% in RCW 108–IR) appear to have optically thick disks as derived from their position in the ( J − H ), ( H − K ) diagram. The disk fraction becomes much higher when IRAC data are employed. The largest fraction of X-ray sources is best described as possessing some disk material via a more detailed extinction fitting. We fit the bulk of the X-ray spectra as absorbed Raymond–Smith-type plasmas, and find that the column to the RCW 108–IR members varies from 10 21 to 10 23 cm −2 . We find that the field contains 41 candidate O or B stars, and estimate that the total number of pre–main-sequence stars in the field is about 1600 ± 200. Approximately 800 are confined to the 3′ (∼1.1 pc) central region.