Mathematics – Probability
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993stin...9525467q&link_type=abstract
Unknown
Mathematics
Probability
Astronomical Spectroscopy, Cosmic Gases, Far Infrared Radiation, Fine Structure, Intergalactic Media, Molecular Clouds, Photodissociation, Submillimeter Waves, Chemical Composition, Emission Spectra, Photons, Temperature Distribution
Scientific paper
The physical properties of the galactic and extragalactic photodissociation regions, warm gas components molecular clouds are, generally, derived through the far-infrared (FIR) fine structure and submillimeter line emissions arising out of these regions. In the theoretical studies of these lines the model of Tielens and Hollenbach (herein after referred as TH) are usually employed in which all the opacity is assumed local in escape probability formalism and inward directed photons do not escape. These assumptions are contrary to the observational facts, where most of the lines are found optically thin except OI (63 micro m) and low rotational transitions of CO and some other molecules. The optically thin medium will allow the radiation to escape through any face of the region. These observational evidences let us to assume finite parallel plane slab, instead of semi-infinite parallel slab, in which the photons are allowed to escape from both surfaces (back and front). In the present study an attempt has been made to incorporate the two sided escape of photons from the PDR's and to study its effect on the FIR and submillimeter line emission from the PDR's/molecular clouds. Further the present formalism is also employed to study the clumpy PDR's/molecular clouds. The preliminary results show that now serious consequences are found on the thermal and chemical structure of the regions but individual line emissions are modified by differing factors. Particularly at low density and low kinetic temperature the change is substantial but at density greater than the critical density of the line and temperature close to the excitation temperature its effect is almost negligible. An attempt has also been made to study the physical conditions of the M17 region employing the present formalism.
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