The Abundance of Helium Relative to Hydrogen in the Orion Nebula

Citation

Mathis, John Samuel (1956) The Abundance of Helium Relative to Hydrogen in the Orion Nebula. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/CB4D-4026. https://resolver.caltech.edu/CaltechETD:etd-06072004-163340

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Spectrograms were taken at two slit positions in the brighest portion of the Orion Nebula near the exciting star [...] Ori C. Four independent measurements were made in each slit position of the ratios of the He I lines [...], and [...] to the hydrogen lines H , H , and H , respectively. The ratios of the [OIII] lines [...] and [...] and of the [OII] lines [...] and [...] were also determined. Reddening by interstellar absorption was taken into account. The electron density was found from the [OII] lines to be 3,800 [...]. The electron temperature was found from the [OIII] lines to be 10,000[degrees]K. The theory of statistical equilibrium was developed for neutral helium, and from the three helium lines the ratio of abundances of helium and hydrogen was found to be 0.128 by number. All three lines gave results within nineteen per cent of the average in both slit positions. It was found that the absorption of the line of He I at [...] in the spectrum of [...] Ori, C could take place in only .025 parsec under the most favorable conditions. In order to estimate the lifetime of the [...] level in helium the probability of two-photon emission was estimated. The estimate was [...].

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