Interpretation of the surface brightness of dark nebulae.
Abstract
The surface brightness measurements of the author (Mattila, 1970) in two dark nebulae, the Coalsack and a dark nebula in Libra, are interpreted in terms of the albedo and the form of the scattering function of the interstellar particles. In a theoretical study on radiative transfer in spherical models for interstellar dust clouds the Monte Carlo method is used to find the intensity of the scattered light for a parallel beam of incident light. The illumination of dark nebulae by the Milky Way is then discussed, and theoretical values of the scattered light are calculated for the various particle models. Then, a comparison with the observations gives the albedo a and the asymmetry factor g of the interstellar particles in an unambiguous way, when it is assumed that the Coalsack and the Libra Cloud consist of the same kind of particles. Their values are found to be: a = 0.65, g = 0.85, with an uncertainty of about + 0.1 for both. A reinterpretation of Witt's observations of the diffuse galactic light in Cygnus and Taurus-Auriga is presented, and it gives support to these values. Key words: dark nebulae - diffuse galactic light - interstellar particles - radiative trassfer in cosmic dust clouds
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 1970
- Bibcode:
- 1970A&A.....9...53M