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Session 18 - The Interstellar Medium.
Oral session, Monday, June 08

[18.06] The Interstellar Gas Toward SN1987A

D. G. York, D. Welty, P. C. Frisch (U. Chicago), G. Sonneborn (GSFC)

The IUE high resolution spectra of SN 1987A contain a number of interstellar absorption lines. Using ground-based observations at extremely high resolution for Ca II and Na I, a model for the distribution of interstellar gas, in velocity space, is derived. Applying the model to the IUE profiles allows extraction of the relative abundances (relative to Zn) of C, Mg, Al, Si, P, Cl, Ti, Cr, Mn, Fe and Ni. While we cannot derive absolute abundances (relative to hydrogen), the results are generally consistent with such abundances derived for stars and H II regions in the LMC, combined with reasonable depletions in the interstellar gas. The UV spectra do not allow study of individual components, so averages are taken over each of 10 aggregates of cloud components containing a total of 44 components in optical spectra of Na I and Ca II. To within the constraints imposed by these practical limitations, the main findings are these. First, the LMC clouds contain no detectable gas that is depleted as in cold clouds in the Galaxy. Second, some clouds have depletion patterns similar to those seen in QSO absorption line systems. The study confirms the galactic gas classification system found for the star SK 108 in the SMC.

Program listing for Monday