Grain Processing in YSO Disks
          Benjamin A. Sargent, Univ. of Rochester
          William J. Forrest, Univ. of Rochester
          Paola D'Alessio, CRYA UNAM
          Nuria Calvet, SAO
          Elise Furlan, Cornell Univ.
          Lee Hartmann, CfA
          Keven I. Uchida, Cornell Univ.
          Greg C. Sloan, Cornell Univ.
          Christine H. Chen, JPL
          Francisca Kemper, UCLA
          Dan M. Watson, Univ. of Rochester
          Joel D. Green, Univ. of Rochester
          Luke D. Keller, Ithaca College
          Terry L. Herter, Cornell Univ.
          Bernhard R. Brandl, Leiden Univ.
          James R. Houck, Cornell Univ.
          Don J. Barry, Cornell Univ.
          Patrick W. Morris, SSC
          Joan Najita, NOAO
          Phil C. Myers, SAO

          Forrest et al. (2004) presented 5-30 micron Spitzer Infrared Spectrograph observations of six SED Class II YSOs in Taurus.  All of the sources have broad 10 micron silicate emission features.  Each one has a unique shape, indicating variation in composition and crystallinity of the silicate grains in the circumstellar disks of these 6 YSOs.  One of the sources, CoKu Tau /4, which apparently has very little disk material out to ~10 AU, has a very smooth and narrow 10 micron emission feature, indicating the silicate grains composing its disk are amorphous and simple.  The spectra of the other five sources, all of which have accretion disks with inner radii much less than ~1 AU, have more structured 10 micron features, indicating the presence of crystalline silicates, which are believed to arise from processing of amorphous silicates.  This processing apparently has not occurred for CoKu Tau /4, where the observable dust is cool (~122K).  The dust emissivity is derived from the observed spectra and compared to grain models.  For CoKu Tau /4, nonspherical amorphous olivine and pyroxene grains are indicated. These grains are believed to be unprocessed material; as such, they represent a primordial mixture from which to base the silicate emission modeling for other sources.  For the sources with more complexity (FM Tau, IP tau, GG Tau, FN Tau, and CY Tau in order of complexity), crystalline forsterite, enstatite, and larger grains are added to fit the spectra.