Applicability of the discrete-dipole approximation to light-scattering simulations of large cosmic dust aggregates

¹ Institut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany e-mail: koehlert@uni-muenster.de
² Institute of Low Temperature Science, Hokkaido University, Kita-ku Kita-19 Nishi-8, Sapporo 060-0819, Japan

Received: 28 April 2005
Accepted: 11 October 2005

Abstract

Light-scattering properties of cosmic dust particles depend on the structure and composition of the particles. A common model assumption of cosmic dust particles that is consistent with observational data is to describe them as aggregates consisting of irregularly shaped, inhomogeneous, submicron-sized monomers. It is necessary for a study of their optical properties to apply a proper light-scattering theory, in which we can fully take this shape and structure of particles into account. Among currently available light-scattering theories, the discrete-dipole approximation (DDA) with the lattice dispersion relation (LDR) is the best method to simulate light scattering by aggregates of such complex structures. We investigate the accuracy of the LDR-DDA method with large aggregates consisting of spherically shaped, homogeneous, identical monomers of 0.1 μm in radius, for which rigorous solutions are known. The asymmetry parameter and single-scattering albedo of these aggregates are here computed with the LDR-DDA method as well as the superposition T-matrix method. We find that the conditions previously given in the literature to calculate cross sections of spherical particles within the accuracy of a few percent are also suitable for large aggregates. We discuss the required computer memory that restricts simulating the optical properties of the considered aggregates.