Interstellar Grains: Effect of Inclusions on Extinction

TL;DR

This paper develops a composite dust grain model with silicate hosts and graphite inclusions to explain interstellar extinction, polarization, IR emission, and abundance constraints, using discrete dipole approximation to match observed curves.

Contribution

It introduces a new composite grain model combining silicate and graphite, evaluated with DDA, to better match interstellar extinction observations.

Findings

Model successfully reproduces observed extinction curves

Composite grains explain polarization and IR emission data

Extinction efficiencies vary with grain shape and composition

Abstract

A composite dust grain model which simultaneously explains the observed interstellar extinction, polarization, IR emission and the abundance constraints, is required. We present a composite grain model, which is made up of a host silicate oblate spheroid and graphite inclusions. The interstellar extinction curve is evaluated in the spectral region 3.4-0.1$\mu m$ using the extinction efficiencies of the composite spheroidal grains for three axial ratios. Extinction curves are computed using the discrete dipole approximation (DDA). The model curves are subsequently compared with the average observed interstellar extinction curve and with an extinction curve derived from the IUE catalogue data.