Modelling OH in regions of star formation |
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| Authors: | R C Doel D Field M D Gray R N F Walker |
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| Institution: | (1) School of Chemistry, University of Bristol, U.K.;(2) Dept. of Physics, University of Bristol, U.K. |
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| Abstract: | There is a large, diverse and rapidly growing body of OH observations from regions associated with star formation, the physical conditions of which are of great interest. To interpret these observations we need to calculate the populations of the OH energy levels using as accurate a model as is feasible. We have developed a large velocity gradient (LVG) model using the lowest 48 hyperfine states of OH and including the phenomenon of far-infrared line overlap using a new theory which treats all thermal and velocity overlaps. If we use a theory of maser propagation (Field and Gray, 1988) we are then able to see how competing maser lines develop.The generic behaviour which we find is in good agreement with the extensive maser observations of Gaume and Mutel 1987 and our calculations allow us to associate general physical conditions with the four ground state maser frequencies. In addition we are able to present preliminary results of the interpretation of the OH absorption observations of Guilloteauet al. (1984) and Walmsleyet al. (1986) for the compactHII region DR21.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on  New Windows to the Universe , held 3–8 July, 1989, Tenerife, Canary Islands, Spain |
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