Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-06-22
Astron.Astrophys.441:555,2005
Astronomy and Astrophysics
Astrophysics
10 pages, 6 figure To appear in A & A, 2005
Scientific paper
10.1051/0004-6361:20052707
Observations of interstellar extinction and polarization indicate that the interstellar medium consists of aligned non-spherical dust grains which show variation in the interstellar extinction curve for wavelengths ranging from NIR to UV. To model the extinction and polarization, one cannot use the Mie theory which assumes the grains as solid spheres. We have used a T-matrix based method for computing the extinction efficiencies of spheroidal silicate and graphite grains of different shapes (axial ratios) and sizes and used these efficiencies to evaluate the interstellar extinction curve in the wavelength range 3.4--1.0 microns. A best fit linear combination of silicate and graphite grains of not very large axial ratio, fits the observed extinction curve reasonably well. We calculate the volume extinction factor Vc, which is an important parameter from the point of view of the cosmic abundance, for the spheroidal grain models that reproduce the interstellar extinction curve. We find that the shape of the grains do not affect the volume extinction factor. Finally we have also studied the extinction and linear polarization efficiencies for aligned spheroids. The results show that the shape of grains affects the linear polarization efficiencies considerably for various orientation angles of the spheroids.
Gupta Ranjan
Mukai Tadashi
Okada Yasuhiko
Sen Asoke K.
Vaidya Deepak B.
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