Evolving Optical Properties of Annealing Silicate Grains: From Amorphous Condensate to Crystalline Mineral

Abstract

Laboratory studies of the evolution of a magnesium silicate smoke from an amorphous condensate to a crystalline mineral by annealing in vacuum provide a foundation for the development of a silicate evolution index (SEI). The SEI can be used to predict the emergent IR spectrum of silicate dust in a circumstellar shell based on the time-temperature history of the silicate grains in the out—ow. Optical constants for the magnesium silicate smoke samples compatible with those of Draine & Lee are derived over the range 0.001¨1000 km. Subject headings: circumstellar matterdust, extinctionISM: moleculesmethods: laboratory ¨ molecular processes