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J. Rho, S. Ramirez (SSC/Caltech), M. Corcoran, K. Hamaguchi (NASA/GSFC), B. Lefloch (LAOG, France)
The Trifid Nebula, one of the youngest star-forming HII regions, was observed for 16 hours by the ACIS-I detector on board of the Chandra X-ray Observatory. We detected 304 X-ray sources, thirty percent of which are hard sources, with near-infrared counterparts for two-thirds of the X-ray sources. Chandra resolved the HD164492 multiple system into a number of discrete X-ray sources. X-ray emission is detected from components HD164492A (an O7.5III star which ionizes the nebula), B and C (a B6V star), and possibly D (a Be star). Component C is blended with an unidentified source (we called Component C2, hereafter). HD164492A has a soft spectrum (kT~0.5 keV) while the component C blend shows much harder emission (kT ~6 keV). This blend and other hard sources are responsible for the hard emission and Fe K line seen by the ASCA, which was previously attributed entirely to HD 164492A. The soft spectrum of the O star is similar to emission seen from other single O stars and is probably produced by shocks within its massive stellar wind. Lack of hard emission suggests that neither a magnetically confined wind shock nor colliding wind emission is important in HD164492A. A dozen stars are found to have flares in the field and most of them are pre-main sequence stars (PMS). Six sources with flares have both optical and 2MASS counterparts. These counterparts are not embedded and thus it is likely that these sources are in later stage of PMS evolution, possibly Class II or III. Two flare sources did not have any near-IR, optical, or radio counterparts. We suggest these X-ray flare stars are in an early pre-main sequence stage (Class I or earlier). We also detected X-ray sources apparently associated with two massive star forming cores, TC1 and TC4. The spectra of these sources show high extinction and X-ray luminosities of 2 - 5x 1031 erg s-1. If these source are Class 0 objects, it is unclear if their X-ray emission is due to solar-type magnetic activities as in Class I objects, or some other mechanism.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.