  We compare the infrared colors predicted by theoretical models of
protostellar envelopes and protoplanetary disks with initial observations of
young stellar objects made with the Infrared Array Camera (IRAC) on the Spitzer
Space Telescope (Werner et al. 2004, Fazio et al. 2004). Disk and envelope
models characterized by infall and/or accretion rates found in previous studies
can quantitatively account for the range of IRAC colors found in four young
embedded clusters: S 140, S 171, NGC 7129, and Cep C. The IRAC color-color
diagram ([3.6]-[4.5] vs. [5.8]-[8.0]) can be used to help to distinguish
between young stars with only disk emission and protostars with circumstellar
envelopes.

Astrophysics