Composite interstellar grains
J. S. Mathis, G. Whiffen;
ApJ, 1989, 341, 808
ABSTRACT:The possibility that interstellar grains are composite collections of very small particles, loosely attached to one another, is
investigated.
The grains are assumed to include a substantial proportion of vacuum along
with solid particles.
The optical properties of the composite grains are
calculated with the approximate 'Bruggeman mixing rule', and the extinction of
the grain is calculated wih standard Mie theory.
The derived cross
sections are close to those of hollow spheres in which the constituents occupy
the proper volume fractions, and the derived optical constants of the
mixture also obey the Kramers-Kroenig relations.
The calculated
interstellar extinction law shows reasonable agreement with observations of the
diffuse ISM over the 1500-0.12 micron wavelength range.
The predicted albedo
is 0.5-0.6.
It is predicted that the visual extinction per H nucleus
should increase slightly with R(V).
KEYWORDS: cosmic dust, interstellar extinction, interstellar matter, particle size distribution, amorphous materials, graphite, infrared spectroscopy, silicates
CODE: mathis89