INTERSTELLAR GAS-PHASE ABUNDANCE OF CARBON, OXYGEN, NITROGEN, COPPER, GALLIUM, GERMANIUM, AND KRYPTON TOWARD ZETA-OPHIUCHI

We present an analysis of weak (less than 10 m angstrom) UV interstellar absorption line data obtained with the Goddard High Resolution Spectrograph echelle modes for the line of sight to the O9.5 IV star zeta-Oph. Accurate measures of weak lines of N I], O I], Cu II and a new UV detection of Na I are reported along with a small upper limit for C II]. Reliable interstellar detections of Ga II, Ge II, and Kr I are also presented. Ga, Ge, and Kr represent the heaviest elements detected in the ISM. Comparison of the derived column densities to cosmic abundances shows Ga is depleted by about -1.2 dex while Ge is overabundant by +0.2 dex. However, interpretation of the intrinsic abundances of these predominantly s-process elements is difficult due to possible intrinsic dust depletion and f-value uncertainties. The detection of Kr I is particularly significant since, as a noble gas, it is not expected to form chemical or mechanical bonds and should primarily reside in the gas phase. The derived Kr depletion of -0.3 dex is questionable because of large uncertainties associated with the cosmic abundance. Assuming Kr to be undepleted, we obtain a logarithmic cosmic abundance of [Kr/H] = 2.95 on the scale where [H] = 12.00. Since the formation of Kr is from a mixture of s- and r-process nucleosynthesis, further observations of this important atom will provide significant insights about nucleosynthesis and interstellar enrichment processes.