Effects of grain models on UV penetration into clouds

Details Effects of grain models on UV penetration into clouds Effects of grain models on UV penetration into clouds

Dec 1984

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984mnras.211..719c&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 211, Dec. 1, 1984, p. 719-736.

Astronomy and Astrophysics

Astronomy

18

Astronomical Models, Cosmic Dust, Interstellar Extinction, Interstellar Matter, Reflection Nebulae, Ultraviolet Radiation, Diffuse Radiation, Particle Size Distribution, Spherical Harmonics

Scientific paper

A derivation of the average scattering characteristics of interstellar grains in the ultraviolet based mainly on observations of extinction is shown to be more reliable than a determination from direct measures of scattered light. Several representative scattering models are constructed and their consequences for the transfer of UV radiation in clouds are discussed using the spherical harmonic expansion method (Flannery, Roberge and Rybicki 1980). Because of the presence of large grains (of about 0.15 microns) in the size distribution, all models are characterized by strongly anisotropic scattering throughout UV range (from about 0.7 to 0.9) with a relatively low albedo (less than 0.4 for wavelength greater than 2500 A) resulting from the presence of very small grains (no greater than 0.01 microns). An approximate algorithm replacing the exact solution of the radiative transfer equation by a greatly simplified solution for g = 1 is presented. It is shown to be accurate to within less than 10 percent at low and intermediate optical depths for values of g greater than 0.7 and albedos lower than 0.4 and to give a deviation of less than a factor of 2 for g as low as 0.5.

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