Where have all the interstellar silicon carbides gone?

Abstract

The detection of the 11.3-micron emission feature characteristic of the Si--C stretch in carbon-rich evolved stars reveals that silicon carbide (SiC) dust grains are condensed in the outflows of carbon stars. SiC dust could be a significant constituent of interstellar dust since it is generally believed that carbon stars inject a considerable amount of dust into the interstellar medium (ISM). The presence of SiC dust in the ISM is also supported by the identification of presolar SiC grains of stellar origin in primitive meteorites. However, the 11.3-micron absorption feature of SiC has never been seen in the ISM and oxidative destruction of SiC is often invoked. In this work we quantitatively explore the destruction of interstellar SiC dust through oxidation based on molecular dynamics simulations and density functional theory calculations. We find that the reaction of an oxygen atom with SiC molecules and clusters is exothermic and could cause CO-loss. Nevertheless, even if this is extrapolable to bulk SiC dust, the destruction rate of SiC dust through oxidation could still be considerably smaller than the (currently believed) injection rate from carbon stars. Therefore, the lack of the 11.3-micron absorption feature of SiC dust in the ISM remains a mystery. A possible solution may lie in the currently believed stellar injection rate of SiC (which may have been overestimated) and/or the size of SiC dust (which may actually be considerably smaller than submicron in size).

7 pages, 5 figures; accepted for publication in MNRAS

References in corpus (5)

• The shape and composition of interstellar silicate grains
• Molecular oxygen in the rho Ophiuchi cloud
• The mass-loss, expansion velocities and dust production rates of carbon stars in the Magellanic Clouds
• On the mass and metallicity distribution of parent AGB stars of presolar SiC
• Stellar Pulsation and the Production of Dust and Molecules in Galactic Carbon Stars

Cited by in corpus (4)

• The first detection of SiC${}_2$ in the interstellar medium
• Reconciling spectroscopy with dynamics in global potential energy surfaces: the case of the astrophysically relevant SiC${}_2$
• Formation of ${\text{H}}_2$ on polycyclic aromatic hydrocarbons under conditions of the ISM: an ab initio molecular dynamics study
• The Binding Energies of Atoms on Amorphous Silicate Dust: A Computational Study