THE SILICATES IN THE DISK OF BETA-PICTORIS

We have obtained intermediate-resolution (R almost-equal-to 50) infrar ed (2.6-13.5 mum) spectra Of the particles in the circumstellar disk o f beta Pic. The silicate dust feature near 10 mum is broader and conta ins more structure than interstellar and most circumstellar emission f eatures. The silicate feature in beta Pic is remarkably similar to tho se in comets Halley, Bradfield 1987s, and Levy 1990 XX which have emis sion features characteristic of crystalline silicates. This result sup ports the inference based on IRAS results that cometary bodies resuppl y the grains in the beta Pic disk. Detailed models of the dust disk an d grains are used to derive plausible disk temperature and density gra dients. We discuss implications of these results on the history and st ate of dust in disks and the solar system.