Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989apj...338..162a&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 338, March 1, 1989, p. 162-170. Research supported by NASA.
Astronomy and Astrophysics
Astrophysics
31
Cosmic Dust, Gas Ionization, Graphite, H Ii Regions, Photoabsorption, Silicates, Absorption Spectra, Electron Energy, Interstellar Gas, Photoionization, Radiation Distribution
Scientific paper
Interstellar dust that is present in H II regions will most likely absorb H-ionizing photons more efficiently than He-ionizing photons. Assuming a silicate-graphite dust composition, the effects of such selective absorption on the ionization structure of H, He, O, and N are investigated with emphasis on a blister geometry. Scattering by the dust grains is included in the generalized on-the-spot approximation. For a relatively soft radiation field of effective temperature about 35,000 K, the radiation hardening may cause the He(+) zone to be nearly coextensive with the H(+) zone, and the O(++) volume is strongly increased relative to the N(++) volume. The smaller grains (radii about 0.005 micron) contribute most to the selective absorption. We show that because of a cancellation of effects a simple analytical formula for the fraction of ionizing photons absorbed by the dust given by Petrosian, Silk, and Field is quite accurate in the case of silicate-graphite dust, even for blister regions.
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