EXTINCTION AND POLARIZATION OF TRANSMITTED LIGHT BY PARTIALLY ALIGNED NONSPHERICAL GRAINS

The problem of model theoretical calculation of the interstellar extinction and polarization due to non-spherical grains partially aligned in a magnetic field is considered. The Waterman's T-matrix approach is used to develop a rigorous analytical method to average the extinction matrix over orientations of a nonspherical grain. The method results in minimizing the numerical effort and can be used for efficient numerical calculations in the resonance region of grain size parameters. Numerical aspects of the proposed method are discussed in detail. The range of validity of the Rayleigh approximation in calculating the extinction matrix for partially aligned spheroidal grains is examined, i.e., the values of the equal-volume-sphere size parameter are determined below which the Rayleigh-limit formulae are accurate within a given error.