AAS 205th Meeting, 9-13 January 2005
Session 136 Classy I and II Protostars
Poster, Thursday, January 13, 2005, 9:20am-4:00pm, Exhibit Hall

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[136.07] Grain Processing in YSO Disks

B. Sargent, W. J. Forrest (University of Rochester), P. D'Alessio (CRYA UNAM), N. Calvet (SAO), E. Furlan, L. Hartmann (CfA), K. I. Uchida, G. C. Sloan (Cornell University), C. H. Chen (JPL), F. Kemper (UCLA), D. M. Watson, J. D. Green (U. of Rochester), L. D. Keller (Ithaca College), T. L. Herter (Cornell Univ.), B. R. Brandl (Leiden University), J. R. Houck, D. J. Barry, P. Hall (Cornell Univ.), P. W. Morris (Caltech), J. Najita (NOAO/Tucson), P. C. Myers (SAO)

Forrest et al. (2004) presented 5-30 micron Spitzer Infrared Spectrograph observations of six SED Class II YSO's 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 YSO's. 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 complicated 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 (~122 K). The dust emissivity is derived from the observed spectra and compared to grain models. For CoKu Tau /4, small amorphous spherical olivine grains are indicated. For the sources with more complexity (FM Tau, IP Tau, GG Tau, FN Tau, and CY Tau in order of complexity), additional components of crystalline forsterite, enstatite, and larger grains are needed to fit the spectra.

This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work was provided by NASA through contract number 1257184 issued by JPL/Caltech and the Spitzer Fellowship Program, under award 011 808-001.

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