2008ApJS..176..184F

We present Spitzer Infrared Spectrograph (IRS) spectra of 28 Class I protostars in the Taurus star-forming region. The 5-36 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 shorter and 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.