SIMBAD references

We demonstrate that CaO and Ca(OH)₂are excellent candidates to explain the 6.8 µm feature, which is one of the most obscure features in young stellar objects. We discuss the condensation of CaO grains and the potential formation of a Ca(OH)₂surface layer. The infrared spectra of these grains are compared with the spectra of 15 young stellar objects. We note that CaO-rich grains are seen in all meteoritic CAIs (calcium-aluminum-rich inclusions) and that the 6.8 µm feature has only been observed in young stellar objects. Therefore, we consider CaO grains to be a plausible candidate to explain the 6.8 µm feature and hypothesize that they are produced in the hot interiors of young stellar environments.