Chandra Observation of the Trifid Nebula: X-ray emission from the O star complex and actively forming pre-main sequence stars

摘要

The Trifid Nebula, a young star-forming HII region, was observed for 16 hoursby the Chandra X-ray Observatory. We detected 304 X-ray sources, thirty percentof which are hard sources and seventy percent of of which have near-infraredcounterparts. Chandra resolved the HD164492 multiple system into a number ofdiscrete 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 possiblyD (a Be star). HD164492A has a soft spectrum (kT ~ 0.5 keV) while the componentC blend shows much harder emission (kT ~ 6 keV). The soft spectrum of the Ostar is similar to emission seen from other single O stars and is probablyproduced by shocks within its massive stellar wind. Lack of hard emissionsuggests that neither a magnetically confined wind shock nor colliding windemission is important in HD164492A. A dozen stars are found to have flares inthe field and most of them are pre-main sequence stars (PMS). Six sources withflares have both optical and 2MASS counterparts. These counterparts are notembedded and thus it is likely that these sources are in a later stage of PMSevolution, possibly Class II or III. Two flare sources did not have anynear-IR, optical, or radio counterparts. We suggest these X-ray flare stars arein an early pre-main sequence stage (Class I or earlier). We also detectedX-ray sources apparently associated with two massive star forming cores, TC1and TC4. The spectra of these sources show high extinction and X-rayluminosities of 2 - 5 x 10^{31} erg/s. If these sources are Class 0 objects, itis unclear if their X-ray emission is due to solar-type magnetic activities asin Class I objects, or some other mechanism.