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1998ApJ...499..799L - Astrophys. J., 499, 799-809 (1998/June-1)
Near-infrared spectroscopy of photodissociation regions: the Orion bar and Orion S.
LUHMAN K.L., ENGELBRACHT C.W. and LUHMAN M.L.
Abstract (from CDS):
In addition, we have observed the strongest ∼30 near-IR He I emission lines, many of which have not been detected previously. There is good agreement between most observed and theoretical He I line ratios, while a few transitions with upper levels of n 3P (particularly 4 3P-3 3S 1.2531 µm) are enhanced over strengths expected from collisional excitation. This effect is possibly due to opacity in the UV series n 3P-2 3S. We also detect several near-IR [Fe II] and [Fe III] transitions with line ratios indicative of low densities (ne ∼ 103-104 cm–3), whereas recent observations of optical [Fe II] emission imply the presence of high-density gas (ne ∼ 106 cm–3). These results are consistent with a model in which high-density, partially-ionized gas is the source of the iron transitions observed in the optical, while low-density, fully-ionized material is responsible for the near-IR emission lines.
Abstract Copyright: ∼
Journal keyword(s): Infrared: ISM: Lines and Bands - ISM: Individual: Name: Orion Nebula - ISM: Molecules - ISM: Structure
Nomenclature: [LEL98] Bar N (Nos 1-3).
Simbad objects: 9
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