K. Chamaillard et Jpj. Lafon, Statistical approach of the effects of roughness on the polarization of light scattered by dust grains, J QUAN SPEC, 70(4-6), 2001, pp. 519-528
Citations number
19
Categorie Soggetti
Spectroscopy /Instrumentation/Analytical Sciences
Journal title
JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER
In order to study the effect of shape on the optical properties of dust gra
ins, we statistically analyze the linear polarized scattered light. We star
t by examining a homogeneous spherical grain using the discrete dipole appr
oximation (DDA) Draine (Astrophys J 1988;333:848). Using a uniform law we r
emove elements of matter on the surface of the grain to describe a random r
oughness. Then, for various scattering angles, the linear polarization P-1
is calculated. We successively repeat the simulation in order to obtain a s
ample of random variables constituting the values P-1 of the linear polariz
ation. The analysis of the results is then achieved through a Gaussian kern
el method which provides the probability density function of P-1 for each s
cattering angle. We present the results for a typical interstellar grain of
water-ice with radius a comparable to the incident wavelength lambda so th
at the parameter size x drop 2 pia/lambda similar or equal to 1. We apply t
his method for two wavelengths in the near IR, when water-ice is transparen
t at 1.9 mum, and, when water-ice is absorbing at 3.1 mum. We find that the
shape of the density function of the linear polarization is asymmetric to
the mean value of the density function and non-unimodal for several scatter
ing angles. This allows us to separate the effects of roughness from those
of volume. When water-ice is absorbing, we also observe a significant shift
of the polarization peak toward greater scattering angles. (C) 2001 Publis
hed by Elsevier Science Ltd.