Silicate Composition of the Interstellar Medium

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 9.7μm 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 ζ 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.

12 pages, 8 figures

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• Silicon and hydrogen chemistry under laboratory conditions mimicking the atmosphere of evolved stars
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• Modelling the evolution and influence of dust in cosmological simulations that include the cold phase of the interstellar medium
• Dust changes in Sakurai's Object: new PAHs and SiC with coagulation of submicron-sized silicate dust into 10 micron-sized melilite grains
• The rotational disruption of porous dust aggregates from ab-initio kinematic calculations
• Protostars at Subsolar Metallicity: First Detection of Large Solid-state Complex Organic Molecules in the Large Magellanic Cloud
• Infrared Excess of a Large OB Star Sample
• Mid-Infrared Polarization of the Diffuse Interstellar Medium toward CygOB2-12
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• Chandra X-ray Measurement of Heavy Element Abundances of Wolf-Rayet Stars in the Galactic Center
• Photometric Mapping of Carbonaceous/Siliceous Dust and Water Ice in the ISM with JWST: Applications to the Dense Sightlines
• The Binding Energies of Atoms on Amorphous Silicate Dust: A Computational Study