Silicate Composition of the Interstellar Medium

TL;DR

This study investigates the silicate composition of interstellar dust, revealing the presence of non-stoichiometric amorphous silicates, termed 'polivene', which bridge olivine and pyroxene, enhancing understanding of dust evolution in space.

Contribution

The paper introduces models of amorphous silicate dust with intermediate stoichiometry, providing new insights into interstellar dust composition beyond traditional olivine and pyroxene assumptions.

Findings

Evidence for non-stoichiometric amorphous silicates ('polivene') in interstellar dust.

Interstellar silicate dust has stoichiometry between olivine and pyroxene.

Comparison with protoplanetary disk models suggests dust processing in different environments.

Abstract

The composition of silicate dust in the diffuse interstellar medium and in protoplanetary disks around young stars informs our understanding of the processing and evolution of the dust grains leading up to planet formation. Analysis of the well-known 9.7{\mu}m feature indicates that small amorphous silicate grains represent a significant fraction of interstellar dust and are also major components of protoplanetary disks. However, this feature is typically modelled assuming amorphous silicate dust of olivine and pyroxene stoichiometries. Here, we analyze interstellar dust with models of silicate dust that include non-stoichiometric amorphous silicate grains. Modelling the optical depth along lines of sight toward the extinguished objects Cyg OB2 No. 12 and {\zeta} Ophiuchi, we find evidence for interstellar amorphous silicate dust with stoichiometry intermediate between olivine and pyroxene, which we simply refer to as "polivene." Finally, we compare these results to models of silicate emission from the Trapezium and protoplanetary disks in Taurus.