Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...280..609h&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 280, no. 2, p. 609-616
Astronomy and Astrophysics
Astrophysics
34
Cosmic Dust, Granular Materials, Interstellar Extinction, Polarized Light, Porous Materials, Silicates, Stellar Envelopes, Absorptivity, Astronomical Polarimetry, Chemical Composition, Discrete Functions
Scientific paper
The discrete dipole approximation method is used to compute the polarization due to dichroic extinction caused by porous non-spherical dust grains. We investigate especially the influence of porous structures on the polarization of light in the 10 and 18 micrometers silicate features. Here, we found that compact oblate grains give a better fit to the 10 and 18 micrometers observed polarization of the massive young stellar object AFGL 2591 than prolate grains. The increase of the porosity results in an increase of the 18 to 10 micrometers peak polarization ratio as desired for fitting the observed polarization with the BN object, but also in a shift of the peak polarization to longer wavelengths. For a given filling factor, the internal structure of the grains affects both the 18 to 10 micrometers peak polarization ratio and the peak wavelengths of the polarization features, whereas the extinction does not show any remarkable changes in the slope and strength in this wavelength region. We found that the compact oblate grains give still the better fit to the polarization data compared with the porous particles. However, also these particles fail to reproduce the red wing of the 10 micrometers polarization features and the variation in the band ratios. Our study shows that we need optical constants which produce narrower bands and higher band ratios.
Henning Th
Stognienko R.
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