Atomic and molecular interstellar absorption lines toward the high galactic latitude stars HD 141569 and HD 157841 at ultra-high resolution

We present ultra-high-resolution (0.32 bm s(-1)) spectra obtained with the 3.9 m Anglo-Australian Telescope (AAT) and Ultra-High-Resolution Facility ( UHRF) of interstellar Na I D1, Na I D2, Ca II K, K I and CH absorption towa rd two high Galactic latitude stars HD 141569 and HD 157841. We have compar ed our data with 21 cm observations obtained from the Leiden/Dwingeloo H I survey. We derive the velocity structure and column densities of the clouds represented by the various components and identify the clouds with ISM str uctures seen in the region at other wavelengths. We further derive abundanc es, linear depletions, and H-2 fractional abundances for these clouds where ver possible. Both stars are located in regions of IRAS 100 mu m emission a ssociated with high Galactic latitude molecular clouds (HLCs): HD 141569 li es, in projection, close to MBM 37 and the Lynds dark cloud L134N, whereas HD 157841 is in the vicinity of the MBM 151. Toward HD 141569 we detect two components in our UHRF spectra: a weak, broad b = 4.5 km s(-1) component a t -15 km s(-1), seen only in Ca rr K absorption, and another component at 0 km s(-1), seen in Na I DI, Na I D2, Ca II K, K I, and CH absorption. The c loud represented by the -15 km s(-1) component is warm and may be located i n a region close to the star. The cloud represented by the 0 km s(-1) compo nent has a Ca linear depletion delta(Ca) = 1.4 x 10(-4) and shows evidence for the presence of dust, consistent with strong 100 mu m emission seen in this region. The H-2 fractional abundance f(H-2) derived for this cloud is 0.4, which is typically what is observed toward HLCs. We conclude that this 0 km s(-1) cloud is associated with MBM 37 and L134N based on the presence of dust and molecular gas (CH) and good velocity agreement with CO emissio n from these two clouds. This places HD 141569 beyond MBM 37 and L134N, whi ch are estimated to be at approximate to 110 pc. In the case of the HD 1578 41 sight line, a total of six components are seen on our UHRF spectra in Na I D1, Na I D2, Ca II K, K I, and CH absorption. Two of these six component s are seen only in a single species. The cloud represented by the component s at 1.85 km s(-1) has a Ca linear depletion delta(Ca)= 2.8 x 10(-4), indic ating the presence of dust. The f(H-2) derived for this cloud is 0.45, and there is good velocity agreement with CO emission from MBM 151. To the best of our knowledge, this 1.85 km s(-1) component toward HD 157841 is the fir st one found to have relative line widths that are consistent with pure the rmal broadening only. We associate the 1.85 km s(-1) cloud seen in our UHRF spectra with MBM 151 and conclude that HD 157841 must lie beyond similar t o 200 pc, the estimated distance to MBM 151.