  We model the IR Spectral Energy Distribution of circumstellar disks embedded
in a HII region and photoevaporated by the external UV radiation. The model
applies to the photoevaporated disks (proplyds) in Orion Nebula. First we
calculate the IR emission of a PMS star surrounded by a dusty globule that is
immersed within an HII region. The globule is assumed to be spherical,
homogeneous, optically thin in the IR and photoevaporated according to the
Dyson (1968) model. Second, we consider the IR emission of a disk directly
exposed to the nebular environment. The disk is passive and treated according
to the Chiang and Goldreich (1997) model. We improve over the CG97 treatment by
tracing the propagation of the various radiative fluxes through the disk
superheated atmosphere. Since the opposite disk sides receive different amounts
of radiation, the flaring angle and the surface temperature distributions are
different, resulting in well distinguished SEDs for the two disk faces.
Finally, we combine the globule and disk models to estimate the IR emission of
proplyds. The energy input from the central star and the nebular environment
increase the disk flaring angle, and therefore also the amount of stellar
radiation intercepted by the disk. The relative intensity of the disk vs.
envelope emission varies with the tilt angle relative to the directions of
th1Ori-C, and of the Earth. We explore the dependence of the SEDs upon the tilt
angle with respect to the Earth, the distance from th1Ori-C, the size on the
envelope, the inner disk radius and the temperature of the central star. The
resulting SEDs are characterized by a broad peak of emission at 30-60micron,
and are in general significantly different from those of isolated disks in
low-mass star forming regions like Taurus-Auriga.
