  We examine the observational consequences of partial gaps being opened by
planets in protoplanetary disks. We model the disk using a static alpha-disk
model with detailed radiative transfer, parametrizing the shape and size of the
partially cleared gaps based on the results of hydrodynamic simulations.
Shadowing and illumination by stellar irradiation at the surface of the gap
leads to increased contrast as the gap trough is deepened by shadowing and
cooling and the far gap wall is puffed up by illumination and heating. In
calculating observables, we find that multiple scattering is important and
derive an approximation to include these effects. A gap produced by a 200
M_Earth (70 M_Earth) planet at 10 AU can lower/raise the midplane temperature
of the disk by up to ~-25/+29% (~-11/+19%) by shadowing in the gap trough and
illumination on the far shoulder of the gap. At the distance of Taurus, this
gap would be resolvable with ~0.01" angular resolution. The gap contrast is
most significant in scattered light and at thermal continuum wavelengths
characteristic of the surface temperature, reducing or raising the surface
brightness by up to order of magnitude. Since gaps sizes are correlated to
planet mass, this is a promising way of finding and determining the masses of
planets embedded in protoplanetary disks.
