  Physical models of circumstellar disks surrounding pre-main sequence stars
are currently constrained primarily by the spectral energy distribution (SED)
of the system. Here we present first results from a survey of nearby Herbig Ae
stars using nulling interferometry. We measure the spatial extent of the mid-IR
emission for the stars HD 150193, HD 163296, and HD 179218. The results
indicate the size of mid-infrared emission around Herbig Ae stars may be much
smaller than current models predict. The observations constrain ~90% of the 10
micron flux to be within an approximately 20 AU diameter region, providing
significant spatial limits for disk models. These results demonstrate the
scientific potential for nulling interferometry to study circumstellar disks
with better spatial discernment than is possible with standard mid-infrared
imaging.
