Composition of Interstellar Clouds in the Disk and Halo. III. HD 149881

The spectrum of HD 149881, a halo star 1300 pc above the Galactic plane, has been analyzed, based on high-resolution GHRS data from Hubble Space Telescope (HST) together with 21 cm emission observations and profiles of Na I and Ca II features. The results reveal 11 absorption components, of which nine are produced in H I regions, with log N(H⁰ in each region mostly approximately 19.5; one component clearly originates in an H II region. Detailed column densities show that (D(Zn)), the absolute value of the depletion D, for Zn, like that for S, does not much exceed 0.1 dex. With Zn used as a standard of reference, D(Fe) varies from -1.1 to -0.6 dex; (D(Cr)) and (D(Mn)) average less than (D(Fe)) by about 0.1 and 0.2 dex, respectively, with dispersions of about 0.1 dex in this difference. As in Papers I and II, the measured D(Si) is consistent with a 2 to 1 ratio of Fe to Si atoms in grains. The kinetic temperature is these H I regions varies widely among components. Maximum temperatures, found from the widths of 21 cm emission components, range from about 100 to 10,000 K, while actual temperatures, found by comparing the H I widths with the b-values for the ultraviolet features, are about equal or less than 1000 K for six of the H I components. In contrast, toward the halo star HD 93521, temperatures of about 6000 K were found for most of the components. With use of these HD 149881 temperatures, values of n_e were obtained from the ionization equilibrium of Ca(+) and also of Na(0). These values range over an order of magnitude, from about 4.9 x 10^-2 to 1.3 x 10^-3/cu cm, systematically smaller (but also less certain) than in HD 93521. For the low values of n_e found in the coldest components, the electrons can be accounted for by ionization of C atoms, if n_H approximately equals 10/cu cm. For the warmest component, an ionization probability of beta(H⁰) approximately equals 3 x 10^-15/s is required, with lower values for other H I components.