  When studying the evolutionary stages of protostars that form in clusters,
the role of any intracluster medium cannot be neglected. High foreground
extinction can lead to situations where young stellar objects (YSOs) appear to
be in earlier evolutionary stages than they actually are, particularly when
using simple criteria like spectral indices. To address this issue, we have
assembled detailed SED characterizations of a sample of 56 Spitzer-identified
candidate YSOs in the clusters NGC 2264 and IC 348. For these, we use spectra
obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope and
ancillary multi-wavelength photometry. The primary aim is twofold: 1) to
discuss the role of spectral features, particularly those due to ices and
silicates, in determining a YSO's evolutionary stage, and 2) to perform
comprehensive modeling of spectral energy distributions (SEDs) enhanced by the
IRS data. The SEDs consist of ancillary optical-to-submillimeter
multi-wavelength data as well as an accurate description of the 9.7 micron
silicate feature and of the mid-infrared continuum derived from line-free parts
of the IRS spectra. We find that using this approach, we can distinguish
genuine protostars in the cluster from T Tauri stars masquerading as protostars
due to external foreground extinction. Our results underline the importance of
photometric data in the far-infrared/submillimeter wavelength range, at
sufficiently high angular resolution to more accurately classify cluster
members. Such observations are becoming possible now with the advent of the
Herschel Space Observatory.
