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

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

Jun 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991apj...374..580b&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 374, June 20, 1991, p. 580-609. NSERC-supported research.

Astronomy and Astrophysics

Astrophysics

342

Abundance, H Ii Regions, Helium Ions, Orion Nebula, Hydrogen Ions, Photoionization, Spectrophotometry

Scientific paper

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 + or -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.

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