Abstract
Measurements have been made with an electronographic image tube spectrograph of two helium and three hydrogen lines at twenty nine positions in the dense core of the Orion Nebula.
Values for the helium abundance derived show that a large amount of the helium is neutral. This must be caused by large optical depth variations in the core near partially ionised globules (PIG's).
The total abundance of helium is shown to be in the range
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Dopita, M.A., Elliott, K.H. & Meaburn, J. Electronographic measurements of the ionised helium abundance in the core of the Orion Nebula. Astrophys Space Sci 28, 163–171 (1974). https://doi.org/10.1007/BF00642245
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DOI: https://doi.org/10.1007/BF00642245