Modelling interstellar extinction and polarization with spheroidal grains

We calculate the wavelength dependence of the ratio of the linear polarization degree to extinction (polarizing efficiency) P(lambda)/A(lambda) from the ultraviolet to near-infrared. The prolate and oblate particles with aspect ratios from a/b = 1.1 up to 10 are assumed to be rotating and partially aligned with the mechanism of paramagnetic relaxation (Davis-Greenstein). Size/ shape/orientation effects are analyzed. It is found that the wavelength dependence of P(lambda)/A(lambda) is mainly determined by the particle composition and size whereas the values of P(lambda)/A(lambda) depend on the particle shape, degree and direction of alignment. (C) 2008 Elsevier Ltd. All rights reserved.