Silicon carbide and the origin of interstellar carbon grains

Experimental evidence is adduced for an interstellar carbon grain formation mechanism in which SiC nucleates at higher temperatures than 900-1100 C in a hydrogen atmosphere to furnish a surface for subsequent carbon condensation. Studies comparing the spatial distribution of the 11.2-micron SiC feature, or its spectral shape, with thermal dust emission, may further elucidate the present relationship. The model is also consistent with recent laboratory studies which have identified grains of SiC as a constituent of primitive meteorites.