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UV radiation fields in dark clouds

Whitworth, Anthony Peter 1975. UV radiation fields in dark clouds. Astrophysics and Space Science 34 (1) , pp. 155-173. 10.1007/BF00646756

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How dark is it inside a dark cloud? If—as is currently believed-interstellar extinction at UV wavelengths is mainly due to scattering with a strongly forward throwing phase-function, the interior of a dark cloud may be much better illuminated at UV wavelengths than its measured extinction would suggest. We consider the penetration of radiation into a dark cloud against scattering and absorption by grains; and we define a new group property for interstellar grains, the exclusion optical depth τd. τd is a measure of the ability of the grains to exclude radiation from the interior of an externally illuminated cloud. Radiation—as measured by the radiation energy density-penetrates the cloud approximately as if against pure absorption only, with effective optical depth τd. Thus τd is a conceptually and numerically useful quantity when estimating the role of UV radiation in the thermal and chemical balance within a dark cloud. Computations are made of the radiation fields in (1200, 4500) Å, at the centres of dark clouds with measured visual extinctions. It is found that even in very dark clouds, the radiation energy density in (1200, 1800) Å may be significant, due to the high grain albedo at these short wavelengths. Paper presented at the Symposium on Solid State Astrophysics, held at the University College, Cardiff, Wales, between 9–12, July, 1974. As from October 1974, Department of Applied Mathematics and Astronomy, University College, Cardiff, Wales Astrophysics and Space Science Astrophysics and Space Science Look Inside

Item Type: Article
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Publisher: Kluwer Academic
ISSN: 0004-640X
Last Modified: 04 Jun 2017 05:03

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