The optical data can be used to model the UV lines, however, to obtain detailed abundances and physical conditions for individual clouds. The Diffuse Interstellar Clouds toward 23 Orionis. See also recent papers by Meyer, Lauroesch, Crawford, and collaborators. In the ISM, elements heavier than H and He are generally found to be less abundant, relative to H, than they are in the Solar photosphere. The abundances of a number of elements detected for the first time in HST GHRS spectra have clarified the depletion pattern seen in moderately dense interstellar clouds.
Squares identify depletions inferred indirectly from trace ionization stages.
See also recent papers by Cardelli, Meyer, and collaborators. These HV clouds are thus essentially fully ionized. While the total elemental abundances in the HV gas are in some cases uncertain, due to not having data for all potentially significant ionization stages, it appears that Al, Fe, and perhaps Si may still be somewhat depleted, even in gas that has been strongly shocked. Return to top of this page Collaborators on these various projects are L. Hobbs, D. Morton, P. Frisch, J. Lauroesch, D. York, S. Federman, E. Fitzpatrick, E. Jenkins, and J. Raymond.