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FAUST observations in the Fourth Galactic Quadrant*
We analyse UV observations with FAUST of four sky fields in the generaldirection of the Fourth Galactic Quadrant, in which we detect 777 UVsources. This is ~50 per cent more than detected originally by Bowyer etal. We discuss the source detection process and the identification of UVsources with optical counterparts. For the first time in this project weuse ground-based objective-prism information for two of the fields, toselect the best-matching optical objects with which to identify the UVsources. Using this, and correlations with existing catalogues, wepresent reliable identifications for ~75 per cent of the sources. Mostof the remaining sources have assigned optical counterparts but, lackingadditional information, we offer only plausible identifications. Wediscuss the types of objects found, and compare the observed populationwith predictions of our UV Galaxy model.
| Chemical equilibrium from diffuse to dense interstellar clouds. I - Galactic molecular clouds
The present steady state model of interstellar cloud chemicalcomposition involves 1074 reactions among 80 species formed from H, C, Nand O, and includes the heavy elements He, Mg, Si, Fe, and S, due totheir role in the ionization equilibrium. The chemical balance equationsare solved, together with a transfer equation, in a self-consistent way;the transfer equation is solved in each line of the Lyman band to obtainthe photodestruction rate as a function of depth in the cloud. By takingall possible absorbers into account at each frequency, as well as thelarger opacity for nonnormally incident photons, very efficientshielding is obtained, together with an H-H2 transition that is morerapid than that of previous models. The model provides thephotodestruction rates and the densities of the chemical species as afunction of position in the cloud.
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