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Paper: Star Formation in the Orion Nebula II: Gas, Dust, Proplyds and Outflows
Volume: 4, Handbook of Star Forming Regions:
Volume I, The Northern Sky
Page: 544
Authors: O’Dell, C.R.; Muench, A.; Smith, N.; Zapata, L.
Abstract: The visually familiar Trapezium cluster is but one of three centers of recent star formation in the Orion Nebula, with the other two still embedded in its host molecular cloud. The Orion Nebula was produced when the hottest stars in the Orion Nebula Cluster photoionized local gaseous material, forming an open cavity around the Trapezium stars, with a background blister of ionized gas, then a photon dominated region beyond that. On the near side there is a neutral veil of material. The cluster members include many proplyds, young stellar objects that are rendered more visible by being in or near an H II region. Their existence is an argument that the most massive stars in the cluster formed only recently. The second-most luminous star formation center is in the BN-KL region and is embedded in the molecular cloud, which means that it is seen only in X-ray, infrared, and radio wavelengths. There are arguments that it experienced a major energetic event 500–1000 years ago, producing runaway objects and a host of expanding fingers of gas and dust. The third center of star formation, Orion-S, lies only slightly behind the photon dominated region and produces multiple outflows, most of which are bipolar, and are seen in molecular and ionized atomic emission. The proximity of the Orion Nebula and its conditions of low extinction mean that it is the richest region of coll ejecta from pre-main sequence low-mass stars.
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