INTERSTELLAR AND INTERGALACTIC MAGNESIUM AND SODIUM-ABSORPTION TOWARDSN-1993J

We present echelle-resolution (FWHM approximately 5 km s-1) HST observ ations of Mg II, Mg I, and ground-based observations of Na I absorptio n toward SN 1993J which exploded in M81. We detect individual absorpti on components spanning a total velocity range of -163 < upsilon. < + 2 25 km s-1. The components are grouped into three subcomplexes, represe nting absorption from the disk of M81, from our own Galactic disk and halo, and from intergalactic gas which is probably the tidal debris of interactions between M81 and M82. We use the Mg I/Na I ratios to esti mate the temperature of the absorbing gas; many of the components have high ratios, indicative of T > 7000 K, and so originate in the warm, diffuse ionized medium of our own Galaxy, of M81, and of the disrupted ps.