Optical, UV, and X-Ray Scattering by Interstellar Dust Grains

Astrophysics, abstract
astro-ph/0304060

From: Bruce T. Draine <draine@astro.princeton.edu>

Date: Wed, 2 Apr 2003 20:21:25 GMT   (203kb)

Authors:
B.T. Draine

Comments: submitted to ApJ. 36 pages, 18 figures, Latex

Scattering and absorption properties at optical, ultraviolet, and X-ray
wavelengths are calculated for an interstellar dust model consisting of
carbonaceous grains and amorphous silicate grains. The widely-used
Henyey-Greenstein phase function provides a good approximation for the
scattering phase function at wavelengths between ~0.4 and 1 micron, but fails
to fit the calculated phase functions at shorter wavelengths. For lambda < 0.24
micron, the Henyey-Greenstein phase function has an absolute error >50%, and
should not be used for accurate modelling in the vacuum ultraviolet.
Polarization as a function of scattering angle is calculated for selected
wavelengths from the infrared to the vacuum ultraviolet.

The calculations employ realistic dielectric functions with structure near
X-ray absorption edges, with resulting features in absorption, scattering, and
extinction. Differential scattering cross sections are calculated for energies
between 0.3 and 10 keV. The median scattering angle is given as a function of
energy, and simple but accurate approximations are found for the X-ray
scattering properties of the dust mixture, as well as for the angular
distribution of the scattered X-ray halo for dust with simple density
distributions. Observational estimates of the X-ray scattering optical depth
are compared to model predictions. Observations of X-ray halos to test
interstellar dust grain models are best carried out using extragalactic point
sources.

References and citations for this submission:

SLAC-SPIRES HEP (refers to ,
cited by, arXiv reformatted)