Optical observations of three Galactic halo stars: evidence for cloudlets in intermediate- and high-velocity interstellar clouds

Very high resolution (R similar to 160000) absorption line measurements of the interstellar Ca II K and Na I D lines and medium resolution (R similar to 50000) measurements of the interstellar Ti II (3384 Angstrom) line towar ds three Galactic halo stars are presented. The data have signal-to-noise r atios of similar to 90-240. The sightlines studied clearly show several int ermediate-high velocity interstellar clouds with local standard of rest vel ocities in the range similar to -40 to -110 km s(-1). Two different methods have been used to analyze these data. Line profile fitting allows us to mo del multiple components for the different high-velocity clouds separated by only a few km s(-1). The close proximity of the lines in velocity space in dicates that the cloudlets are related. Conversion of the absorption profil es to apparent optical depth profiles also allows us to examine the column densities and their ratios as a function of velocity. Variations in N (Ca I I)/N(Na I), N (Ca II)/N (Ti II) and N (Ti II)/N (Na I) with cloud velocity are discussed.