We analyze samples of Spitzer Infrared Spectrograph spectra of T Tauri stars in the
Ophiuchus, Taurus, and Chamaeleon I star-forming regions, whose median ages lie in the<
1–2 Myr range. The median mid-infrared spectra of objects in these three regions are similar
in shape, suggesting, on average, similar disk structures. When normalized to the same
stellar luminosity, the medians follow each other closely, implying comparable mid-infrared
excess emission from the circumstellar disks. We use the spectral index between 13 and 31 …

We present an analysis of Spitzer-IRS spectra of T Tauri stars in Taurus, Chamaeleon, and
Ophiuchus, which are three nearby star-forming regions of comparable age (1-2 Myr), but
with differing environments. The IRS spectra reveal emission from dust in the inner few AU of
the disk and thus probe the region where planets are thought to form. Our previous study of
the Taurus region showed that significant evolution, like grain growth and settling, is already
occurring in these protoplanetary disks. Here we compare signposts of disk evolution, like …