2004ApJS..154..391W

We present Spitzer Space Telescope Infrared Spectrograph observations in the 5.3-20 µm range of five young stellar objects in Taurus that have Class I continuum spectral energy distributions (λF_λαλⁿ,n≥0), often taken to represent the youngest stellar objects in this star formation region. The spectra include a rich collection of broad absorption features that we identify with amorphous silicates and various ices, notably those of carbon dioxide and water. We show that the absorption features are produced mainly in the envelopes of these systems. The apparent depths of silicate and 15.2 µm CO₂ice features vary among the objects in a manner that is consistent with a variation of inclination with respect to the line of sight, contribution to the silicate features from material throughout the envelopes, and an origin for the CO₂ice feature in the outer parts of the envelope. Thus, these features provide new and useful constraints on models of the physical structure of Class I protostars.