FIRST RESULTS FROM THE UHRF - ULTRA-HIGH-RESOLUTION OBSERVATIONS OF ATOMIC INTERSTELLAR LINES TOWARDS ZETA-OPHIUCHI

We present ultra-high-resolution observations of optical interstellar lines towards zeta Oph obtained during the commissioning phase of the new Ultra-High-Resolution Facility (UHRF) at the AAT. The UHRF has ach ieved its design resolving power of R approximate to 10(6), and has ve ry clearly resolved hyperfine splitting in three of the 11 identified Na I D-line velocity components towards zeta Oph. In addition, the int rinsic line profiles of the 3s-4p Na I doublet at 3302 Angstrom have b een measured for the first time. 12 velocity components are identified in the interstellar Ca II K-line absorption profile, of which seven h ave definite velocity counterparts in the Na I profile. Three of the N a I velocity components have b-values which correspond to a gas temper ature of about 200 K, for the case of pure thermal broadening. The str ongest component in the sightline (-14.8 km s(-1)) was found to have a b-value of 0.6(-0.1)(+0.2) km s(-1), corresponding to a temperature o f 500 K. If a true gas kinetic temperature of 54 K is assumed to apply to this component, from the H-2 rotational excitation temperature pre viously measured for the zeta Oph sightline, then the observed Na I an d Fe I line profiles both imply an rms turbulent velocity of 0.4 km s( -1) within the cloud, just less than the local sound speed. The observ ed Ca II linewidths are all significantly larger than those of the cor responding Na I components. The Ca II components are interpreted as ar ising from warm neutral material (intercloud medium) surrounding coole r clouds, while half of the Na I components arise from cool clouds and half arise from warm intercloud material. The measured Na I/Ca II col umn density ratios, and the inferred temperatures, are consistent with a model in which calcium is heavily depleted on to grains in cool clo uds but is restored to the gas phase by impact desorption in the warm intercloud medium.