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Paper: M20: Star Formation in a Young HII Region
Volume: 5, Handbook of Star Forming Regions:
Volume II, The Southern Sky
Page: 509
Authors: Rho, J.; Lefloch, B.; Reach, W.T.; Cernicharo, J.
Abstract: The Trifid Nebula (M20) has a remarkable optical appearance with a large, reddish nebula of gas ionized by an O7 star (HD 164492) and trisected by obscuring dust lanes, with a blue reflection nebula in the north. During the last two decades, M20 has generated considerable interest because of multi-wavelength identifications of sites of low- and high-mass star formation. M20 is a young HII region showing active, dynamic “pre-Orion” star formation, containing massive, young stars undergoing collapse and violent mass ejection, as well as a dense population of protostars and more developed pre-main sequence stars. Different stages of star formation have been detected at various wavelengths, as well as optical jets, mid- and far-infrared protostars, nearinfrared young stellar objects, Hα emission stars, X-ray sources, and OH masers. M20 is relatively close, at a distance of 1.67 kpc with a low line-of-sight extinction (Av=1.3 mag), and it is compact, with a small diameter of only 3.5 pc. M20 is an isolated HII region with a single O star, which provides an ideal place to investigate the onset of star birth and triggered star formation. We review the highlights of studies of star forming activities in the Trifid Nebula.
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