| Externally Illuminated Young Stellar Objects in the Orion Nebula (2008) | |||||||||||||
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| . The circumstellar material surrounding most low-mass young stars in the Orion Nebula Cluster is rendered visible by the ionizing radiation of the hot Trapezium stars and the background light of M42. I discuss Hubble Space Telescope observations of these lower mass young stellar objects and their environments. Photoionization of circumstellar material by # 1 Ori C produces a bright cusp-shaped ionization front on the side facing the star and tails with ionized skins pointing away. Inside their ionized envelopes, many externally illuminated young stellar objects are surrounded by dark regions seen in silhouette in HÞ and in the transitions of ionized species. In several objects however, the dark regions are bright in the 6300 A [OI] and 2.122¼m H 2 lines. Radio observations indicate that the total mass of the circumstellar material is at most 10 #2 M . The bright Orion proplyds are evaporating and losing mass at rates of order 3 ð 10 #7 to 3 ð 10 #8 M yr #1 . About 50% of the o... | |||||||||||||
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