  We study the effects of an annular gap induced by an embedded proto-planet on
disk scattered light images and the infrared spectral energy distribution. We
find that the outer edge of a gap is brighter in the scattered light images
than a similar location in a gap-free disk. The stellar radiation that would
have been scattered by material within in the gap is instead scattered by the
disk wall at the outer edge of the gap, producing a bright ring surrounding the
dark gap in the images. Given sufficient resolution, such gaps can be detected
by the presence of this bright ring in scattered light images. A gap in a disk
also changes the shape of the SED. Radiation that would have been absorbed by
material in the gap is instead reprocessed by the outer gap wall. This leads to
a decrease in the SED at wavelengths corresponding to the temperature at the
radius of the missing gap material and a corresponding flux increase at longer
wavelengths corresponding to the temperature of the outer wall. We note that,
unlike an inner hole in the disk, the presence of an annular gap does not
change the bolometric IR flux; it simply redistributes the radiation,
previously produced by material within the gap, to longer wavelengths. This
implies that the changes in the SED generally will be smaller for gaps than
holes. Although it will be difficult on the basis of the SED alone to
distinguish between the presence of a gap and other physical effects, the level
of changes can be sufficiently large to be measurable with current instruments
(e.g., Spitzer).
