Extinction Properties of Dust Grains: A New Computational Technique

Abstract

view Abstract Citations (23) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Extinction Properties of Dust Grains: A New Computational Technique Michel, B. ; Henning, Th. ; Stognienko, R. ; Rouleau, F. Abstract The Strong Permittivity Fluctuation Theory (SPFT) is a statistical approach to describe the optical properties of randomly oriented inhomogeneous dust grains. In contrast to most other methods that must calculate the extinction properties of individual particles and then sum the results to obtain ensemble averages, the SPFT starts with ensemble-averaged quantities from the very beginning. Therefore, the computation of the extinction has to be performed only once for a given ensemble. This makes this method especially suitable for astrophysical applications in which grain alignment is not required. We use the SPFT in bilocal approximation (BA) to calculate the orientationally and positionally averaged extinction cross section of dust agglomerates. In the BA, the average extinction cross section of a statistical ensemble of grains depends only on the complex refractive index of the constituent particles, and on the value and spatial correlation of the local density (filling factor) of the material. The BA is tested for the case of agglomerates of spherical grains by comparing its predictions to those of the discrete dipole approximation (DDA) and the generalized Mie theory (GMT), which embodies an exact solution of Maxwell's equations. We find that the BA works well for all size parameters tested (up to 0.6, taking the radius of the individual constituent spheres). We find a very good agreement between the BA, DDA, and GMT for a moderate refractive index (nref = 1.7 + 0.7i, typical of soot or "dirty" silicate cosmic dust analogs in the visual). For a somewhat larger refractive index (nref = 2.5 + 1.5i, typical of graphite in the UV), the BA is of comparable accuracy as the DDA. For the more extreme case of a quasimetallic refractive index (nref = 3.0 + 4.0i), the BA seems to be an inadequate approach. For this case, all methods are pushed to their limit. Publication: The Astrophysical Journal Pub Date: September 1996 DOI: 10.1086/177739 Bibcode: 1996ApJ...468..834M Keywords: ISM: DUST; EXTINCTION; METHODS: ANALYTICAL; METHODS: NUMERICAL full text sources ADS |