Unusual, Large-Scale, Motions in HII Regions
In many HII regions, huge volumes of ionized gas emit split lines. Such splitting occurs exclusively over dark areas surrounded by bright rims; these rims, which are produced by ionization fronts eating into the adjacent neutral masses, emit single lines centred on the mean motion of the nebular complex. Detailed observations of this situation are presented for the Orion (M42), Carina, Omega (M17), and 30 Doradus Nebulae. In the latter, Ca+ H and K absorption-line velocities suggest that a HI/HII shell is collapsing toward the central ionizing stars.
KeywordsRadial Velocity Optical Line Line Splitting Large Magellanic Cloud Ionization Front
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