Evolving optical properties of annealing silicate grains: From amorphous condensate to crystalline mineral

Laboratory studies of the evolution of a magnesium silicate smoke from an a morphous 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 c ircumstellar shell based on the time-temperature history of the silicate gr ains in the outflow. Optical constants for the magnesium silicate smoke sam ples compatible with those of Draine & Lee are derived over the range 0.001 -1000 mu m.