Physical conditions in the Orion Nebula and an assessment of its helium abundance

Journal Article · Sat Jun 01 04:00:00 EDT 1991 · Astrophysical Journal; (United States)

DOI:https://doi.org/10.1086/170146· OSTI ID:5193110

Baldwin, J A; Ferland, G J; Martin, P G; Corbin, M R; Cota, S A ^[1]

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1. Ohio State Univ., Columbus (USA) Observatorio Interamericano de Cerro Tololo, La Serena (Chile) Joint Inst. for Lab. Astrophysics, Boulder, CO (USA) Toronto University (Canada)

New long-slit spectrophotometric observations were obtained to redetermine the helium abundance of the Orion Nebula. The ionic ratio He(+)/H(+) is found to remain nearly constant at 0.088 {plus minus} 0.006. In the bright innermost region, the errors are largely systematic due to uncertainties in the reddening curve for Orion grains and deviations from case B emissivity. In the outer regions, the errors are dominated by statistical errors. Photoionization models are computed to determine the correction for the unobserved presence of neutral helium in regions where hydrogen is ionized. 114 refs.

• OSTI ID: 5193110
• Journal Information: Astrophysical Journal; (United States), Journal Name: Astrophysical Journal; (United States) Vol. 374; ISSN ASJOA; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
CHARGED PARTICLES
CHEMICAL COMPOSITION
CHEMISTRY
COSMIC RADIO SOURCES
COSMOCHEMISTRY
ELEMENT ABUNDANCE
ELEMENTS
ERRORS
FLUIDS
GASES
H2 REGIONS
HELIUM
HELIUM IONS
HYDROGEN IONS
IONIC COMPOSITION
IONIZATION
IONS
MATHEMATICAL MODELS
NONMETALS
PHOTOIONIZATION
RARE GASES
SPECTROPHOTOMETRY