  We report mid--IR observations of two young stars found in the Taurus dark
cloud spatially resolving for the first time their 10 $\mu$m emission. The
weak-emission T Tauri star DI Tau, tentatively identified by Skrutskie et al.
(1990) on the basis of 12 $\mu$m IRAS data as an object in the process of
dissipating its circumstellar disk, is found to have no infrared excess at a
wavelength of 10 $\mu$m. The nearby classical T Tauri star DH Tau exhibits
excess emission at 10 $\mu$m consistent with predictions based on circumstellar
disk models. While both objects appear to have the same stellar mass, age, and
rotation rate, they differ in two fundamental respects: DH Tau is a single star
with an active accretion disk and DI Tau is a binary system lacking such a
disk. The companion to DI Tau has a very low luminosity and is located at a
projected distance of $\sim 20$ A.U. from the primary. Assuming the system to
be co-eval, we derive a mass below the hydrogen burning limit for the
companion. We speculate that the formation of a sub-stellar mass companion has
led to the rapid evolution of the circumstellar disk that may have surrounded
DI Tau.
