SpitzerIRS Observations of FU Orionis Objects

We present 5-35 $\mu$m spectra, taken with the Infrared Spectrograph (IRS) onthe Spitzer Space Telescope, of five FU Orionis objects: FU Ori, V1515 Cyg,V1057 Cyg, BBW 76, and V346 Nor. All but V346 Nor reveal amorphous silicategrains in emission at 10 $\mu$m and 20 $\mu$m, and show water-vapor absorptionbands at 5.8 and 6.8 $\mu$m and SiO or possibly methane absorption at 8 $\mu$m.These absorption features closely match these bands in model stellarphotospheres -- signs of the gaseous photospheres of the inner regions of theseobjects' accretion disks. The continuum emission at 5-8 $\mu$m is alsoconsistent with such disks, and, for FU Orionis and BBW 76, longer-wavelengthemission may be fit by a model which includes moderate disk flaring. V1057 Cygand V1515 Cyg have much more emission at longer wavelengths than the others,perhaps evidence of substantial remnant of their natal, infalling envelopes.Comment: 30 pages, 8 figures, accepted by Ap