On the abundance of silicon carbide dust in the interstellar medium

Silicon carbide (SiC) dust is known to be present in carbon-rich stellar ejecta, and SiC particles of probable extra-Solar-System origin have recently been isolated in C-type meteorites. However, solid SiC has never been identified in the interstellar medium, which is remarkable, as the intrinsic strength per Si atom of the Si-C infrared vibrational feature is comparable with that of the corresponding Si-O feature in silicates, observed in many lines-of-sight. We re-examine spectral evidence relevant to the possible existence of SiC in the diffuse interstellar medium, using the line-of-sight to the Galactic Centre as a basis for discussion. We deduce that the abundance of Si in SiC dust is no more than ∼ 5 per cent of that in silicates. Consequently, SiC particles probably contribute at most a few per cent of the total extinction at visible and ultraviolet wavelengths. (author)