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The Ionization of Planetary Nebulae

Published online by Cambridge University Press:  14 August 2015

Robert E. Williams
Robert E. Williams*
Affiliation:
Steward Observatory, University of Arizona, U.S.A.

Abstract

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The ionization of the most abundant elements in planetary nebulae has been determined for a number of models of nebulae at different epochs in their expansion. The values used for the temperatures and radii of the central stars and the sizes and densities of the shells have come from Seaton's evolutionary sequence. The ionizing radiation field has been taken from model atmosphere calculations of the central stars by Gebbie and Seaton, and Böhm and Deinzer. Emission-line fluxes have been calculated for the models and compared with observations of planetary nebulae by O'Dell, Osterbrock's group, and Aller and his collaborators. Results indicate that the central stars have strong He+ Lyman continuum excesses, similar to those predicted by Gebbie and Seaton. The mean abundance determinations for the nebulae made by Aller are confirmed, with the exception of nitrogen, which appears to be 3 or 4 times more abundant than his value. It is also seen that the electron temperatures of the nebulae are higher than previous theoretical determinations, providing better agreement with empirically derived values.

Type
Session III – Physical Processes
Information
Symposium - International Astronomical Union , Volume 34: Planetary Nebulae , 1968 , pp. 190 - 204
Copyright
Copyright © Reidel 1968 

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