CA-II AND CH+ INTERSTELLAR ABSORPTION OBSERVATIONS IN THE DIRECTION OF RESOLVABLE BINARY STARS

We report the initial results of a study to probe the small-scale stru cture in diffuse interstellar clouds by observing optical absorption l ines of CH+ at 4232 Angstrom and Ca II K at 3933 Angstrom towards both components in resolvable binary systems. The data analysis is still i n progress. To date, 70% of the Ca II spectra have been analyzed for t he 19 observed systems. For half of these, a difference in the line st rength or in the number of calcium components is found. The sightlines have been selected so that the observing method provides a potential probe of the small-scale structure of the interstellar medium in the r ange 200-4000 AU.