  We present a spatially resolved 894 micron map of the circumstellar disk of
the Butterfly star in Taurus (IRAS 04302+2247), obtained with the Submillimeter
Array (SMA). The predicted and observed radial brightness profile agree well in
the outer disk region, but differ in the inner region with an outer radius of
~80-120 AU. In particular, we find a local minimum of the radial brightness
distribution at the center, which can be explained by an increasing density /
optical depth combined with the decreasing vertical extent of the disk towards
the center. Our finding indicates that young circumstellar disks can be
optically thick at wavelengths as long as 894 micron. While earlier modeling
lead to general conclusions about the global disk structure and, most
importantly, evidence for grain growth in the disk (Wolf, Padgett, &
Stapelfeldt 2003), the presented SMA observations provide more detailed
constraints for the disk structure and dust grain properties in the inner,
potentially planet-forming region (inside ~80-120 AU) vs. the outer disk region
(~120-300 AU).
