As a part of detailed study of Galactic star forming regions, we plan to
complement far-infrared, sub-millimeter, and radio continuum measurements
with ISO observations in the mid-infrared. The main purpose is to obtain
high angular resolution maps in appropriate filters (in the 3-12 microns
region) centered at wavelengths corresponding to the PAH features and
their nearby continuua. The ISOCAM data will give important clues to the
understanding of: (1) distribution of dust grains relevant for transient
heating; and (2) role of small grains vis a vis normal large grains (the
latter responsible for the far-infrared emission). Combining the results
of radio continuum, far-IR and mid-IR can constrain detailed radiation
transfer model parameters leading to the determination of dust properties
and dust distribution etc.
We propose high angular resolution near/mid-infrared imaging of three
ultra compact HII regions / CO clumps. These are not planned to be observed
by the ISO, either under Guaranteed Time or Guest Observer Programmes. The
trans-IRAS band far-infrared observations of these objects in two bands
centered at 130 and 170 micron with angular resolution of about 1' have
already been made using the Tata Institute's (TIFR) 100 cm balloon-borne
telescope.  The HIRES processed IRAS maps of these sources have also been
obtained in all the four bands. Some of these objects show multiple structures
in the TIFR far-infrared maps. The ISO provides an unique opportunity to get
high angular resolution maps of these sources at astrophysically important
wavelengths (centered at PAH features etc). We plan to observe these sources
in 7 filters of ISOCAM, 4 of which (3.3, 6, 7.75 and 11.4 micron) cover PAH
bands and the rest 3, neighbouring wavelengths for comparison. As all the
target sources are quite strong, a very nominal observation time suffices
for this proposal.