We present the Spitzer Infrared Spectrograph ( IRS ) spectrum of SR20 , a 5–10 AU binary T Tauri system in the \rho Ophiuchi star forming region .
The spectrum has features consistent with the presence of a disk ; however , the continuum slope is steeper than the \lambda ^ { -4 / 3 } slope of an infinite geometrically thin , optically thick disk , indicating that the disk is outwardly truncated .
Comparison with photometry from the literature shows a large increase in the mid-infrared flux from 1993 to 1996 .
We model the spectral energy distribution and IRS spectrum with a wall + optically thick irradiated disk , yielding an outer radius of 0.39 _ { +0.03 } ^ { -0.01 } AU , much smaller than predicted by models of binary orbits .
Using a two temperature \chi ^ { 2 } minimization model to fit the dust composition of the IRS spectrum , we find the disk has experienced significant grain growth : its spectrum is well-fit using opacities of grains larger than 1 \mu m. We conclude that the system experienced a significant gravitational perturbation in the 1990s .