Modelling interstellar extinction and polarization with spheroidal grains

TL;DR

This study models how spheroidal interstellar dust grains affect polarization and extinction across ultraviolet to near-infrared wavelengths, considering particle shape, size, and alignment mechanisms.

Contribution

It introduces a detailed analysis of polarization efficiency for spheroidal grains with various aspect ratios, incorporating alignment effects due to paramagnetic relaxation.

Findings

Polarization efficiency depends mainly on particle composition and size.

Shape and alignment degree influence the polarization-to-extinction ratio.

Wavelength dependence is primarily determined by composition and size.

Abstract

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.