Light Scattering by Porous Dust Particles in the DiscreteDipole Approximation
Abstract
Electromagnetic scattering by irregular dust grains and aggregates has long been a challenging problem in various astronomical applications. Only the quite recent advancement in the discretedipole approximation (DDA) have made the problem trackable. We have applied a new iterative method, the quasiminimal residual algorithm, to the system of linear equations arising in the DDA applications. This method is approximately 3 times faster than the standard iterative scheme, conjugate gradient, use with DDA. We apply DDA both to pseudospherical objects, of which we randomly remove different numbers of small scattering elements (dipoles) to model porous grains, and to aggregates of these grains which we believe to properly model fluffy particles. We study both the single particle intensity and linear polarization as a function of the grain size, packing density and the refractive index. Surprisingly, some results for inhomogeneous particles can be matched by the classical Mie theory using a generalized version of the effective medium theory. Some wellknown photometric and polarimetric features of solar system objects seem to follow naturally from the scattering properties of fluffy particles.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 1994
 DOI:
 10.1086/174012
 Bibcode:
 1994ApJ...425..653L
 Keywords:

 Dipole Moments;
 Discrete Functions;
 Interplanetary Dust;
 Light Scattering;
 Mie Scattering;
 Coherent Scattering;
 Conjugate Gradient Method;
 Linear Polarization;
 Radiative Transfer;
 Astrophysics;
 ISM: DUST;
 EXTINCTION;
 INTERPLANETARY MEDIUM;
 POLARIZATION;
 RADIATIVE TRANSFER