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Approximate solutions of radiative transfer in dusty nebulae. 2: Hydrogen and heliumThe ionization structure of hydrogen and helium in dusty nebulae is discussed. The general equations for pure hydrogen nebulae are modified to include helium. An approximate analytic solution is presented for Stroemgren radii of hydrogen and helium in the absence of dust. It is shown that these results, with simple modifications, are also applicable to dusty nebulae where the effective absorption cross section of dust grains varies slowly with frequency in the 1000 to 200A range. No analytic solutions are possible if this cross section varies rapidly with frequency. In this case, however, simple coupled differential equations are derived. Approximate analytic expressions are presented for evaluation of the variation of the fraction of ionizing radiation absorbed by dust and the ratio of the volume emission measures of He II to H II regions with the spectrum of the ionizing source, helium abundance, and absorption properties of dust. The effects of dust on the He III zone are discussed. Results are restricted to spherically symmetric nebulae, but nonuniform gas and dust distributions and clumpiness can be taken into account.
Document ID
19760009908
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Authors
Dana, R. A. (Stanford Univ. CA, United States)
Petrosian, V. (Stanford Univ. CA, United States)
Date Acquired
September 3, 2013
Publication Date
August 1, 1975
Subject Category
Astrophysics
Report/Patent Number
SU-IPR-637
NASA-CR-146392
Accession Number
76N16996
Funding Number(s)
CONTRACT_GRANT: NGR-05-020-510
CONTRACT_GRANT: NSG-2049
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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