Abstract
High resolution observations of Ca II and Na I interstellar line profiles towards four halo B stars are analysed in terms of multicloud models. Stellar CNO lines present in the spectra have been used in conjunction with an LTE model atmosphere programme to derive values of effective temperature and microturbulence. Using these atmospheric parameters, stellar contributions to the interstellar Ca II and Na I profiles have been calculated and removed. The subsequent renormalized interstellar line profiles were analysed to derive information on the radial velocities, internal velocity dispersions and column densities within individual interstellar clouds. The Na I/Ca II ratio decreases from a value of ∼ 2 to ∼ 0.02 with increasing radial velocity; this range is smaller than that found by previous workers using the doublet ratio method. Additionally the stellar CNO lines in the halo stars imply a composition similar to that found for unevolved B stars in the galactic plane.
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