Experimental study of the formation and destruction of carbonates in circumstellar and interstellar environments and their impact on the oxygen depletion in the interstellar medium
Final Report Abstract
Carbonates can be formed in silicates and carbonaceous material, which represent the two primary components of cosmic dust. A significant quantity of carbon and particularly oxygen, can be stored in such inorganic and organic carbonates, which offers a potential solution to the oxygen depletion issue in the interstellar medium. We have performed a systematic study of the carbonate formation in amorphous silicates with pyroxene and olivine stoichiometry and varying Mg/Fe ratios. The investigations were expanded to encompass the formation of carbonate in CaSiO3 and in fullerene-like carbonaceous condensates. The formation rates were determined for various conditions and condensation gas mixtures. Our findings indicate that carbonates are efficiently formed in pure the magnesium silicates and CaSiO₃. However, the formation of carbonate in iron-bearing silicates is significantly suppressed and nearly completely hindered in pure iron silicates. It was demonstrated that the sequestration of oxygen in silicates can be increased by up to 11%–18% through the introduction of carbonates. Emission spectra were calculated for different dust temperatures, thereby providing insights into the observational detectability of these components in the interstellar medium. The destruction of the carbonate groups in the silicates was studied following thermal annealing at temperatures up to 750 °C or irradiation with Lyman alpha photons. Another subproject was the study of the formation of organic carbonates in carbonaceous matter. The exclusive formation of polycarbonates could not be confirmed, but the experimental results indicate an efficient incorporation of oxygen into the fullerene-like carbon structures including carbonate, ester, ether, carbonyl and other oxygen-bearing groups. An oxygen content of 5-8 at% could be derived after the oxygen treatment. The potential astrophysical applications of the project results are discussed.
Publications
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Gas-phase Condensation of Carbonated Silicate Grains. The Astrophysical Journal, 966(2), 191.
Rouillé, Gaël; Schmitt, Johannes; Jäger, Cornelia & Henning, Thomas
