The ionization structure of the Orion Nebula - Infrared line observations and models

Observations of the forbidden O III 52 and 88 microns lines and the forbidden N III 57 microns line have been made at six positions and the forbidden Ne III 36 microns line at four positions in the Orion Nebula to probe its ionization structure. The wavelength of the forbidden Ne III line was measur...

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Bibliographic Details
Published inThe Astrophysical journal Vol. 311; no. 2; pp. 895 - 908
Main Authors Simpson, J. P., Rubin, R. H., Erickson, E. F., Haas, M. R.
Format Journal Article
LanguageEnglish
Published Legacy CDMS University of Chicago Press 01.12.1986
Subjects
Astronomy
Astrophysics
Earth, ocean, space
Exact sciences and technology
H ii regions. Emission and reflection nebulae
Interstellar medium (ism) and nebulae in milky way
Stellar systems. Galactic and extragalactic objects and systems. The universe
Abundance
Models
Orion nebula
Infrared spectrum
Ionization
H II region
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Summary:Observations of the forbidden O III 52 and 88 microns lines and the forbidden N III 57 microns line have been made at six positions and the forbidden Ne III 36 microns line at four positions in the Orion Nebula to probe its ionization structure. The wavelength of the forbidden Ne III line was measured to be 36.009-36.017 microns. Electron densities and abundance ratios of N(++)/O(++) have been calculated and compared to other radio and optical observations. Detailed one-component and two-component (bar plus halo) spherical models were calculated for exciting stars with effective temperatures of 37,000-40,000 K and log g = 4.0 and 4.5. Both the new IR observations and the visible line measurements of oxygen and nitrogen require Teff of no more than 37,000 K. However, the doubly ionized neon requires a model with Teff of at least 39,000 K, which is more consistent with that inferred from the radio flux or spectral type. These differences in Teff are not due to effects of dust on the stellar radiation field but are probably due to inaccuracies in the assumed stellar spectrum. Neon and nitrogen are approximately solar, but oxygen is half-solar in abundance. From the IR O(++) lines, it is concluded that the ionization bar results from an increase in column depth rather than from a local density enhancement.
Bibliography:CDMS
Legacy CDMS
ISSN:0004-637X
1538-4357
DOI:10.1086/164827