Dust grains are produced abundantly in interstellar space, in particular as a byproduct of mass loss by stars. Examples are nova explosions, Wolf-Rayet stars, and virtually all red giant stars. In the course of time, dust grains intermingle with the interstellar medium, they undergo changes in structure, and they become incorporated in such objects as comets and meteoroids. The Principal Investigators (PIs) propose to continue with their current NSF-funded program of infrared observations of astro- physical dust grains. They will determine the chemical compositions, mineral properties, and size distributions of the grains in the three environments in which they are know to occur: stellar systems, interstellar medium, and solar system. Differences in the grains' properties are expected to yield information about the production and processing of condensable elements in the Galaxy due to stellar evolution. The results may help explain why supernova shocks and heating of the interstellar medium by young stars do not destroy interstellar dust, as theory predicts.
