Spitzer Irs Spectra and Envelope Models of Class I Protostars in Taurus

We present Spitzer Infrared Spectrograph spectra of 28 Class I protostars in the Taurus star-forming region. The 5 to 36 μm spectra reveal excess emission from the inner regions of the envelope and accretion disk surrounding these predecessors of low-mass stars, as well as absorption features due to silicates and ices. Together with shorterand longer-wavelength data from the literature, we construct spectral energy distributions and fit envelope models to 22 protostars of our sample, most of which are well-constrained due to the availability of the IRS spectra. We infer that the envelopes of the Class I objects in our sample cover a wide range in parameter space, particularly in density and centrifugal radius, implying different initial conditions for the collapse of protostellar cores. Subject headings: circumstellar matter — stars: formation — stars: pre-main sequence — infrared: stars