ESTIMATION OF THE EQUIVALENT WIDTH OF THE INTERSTELLAR CA-II-K ABSORPTION-LINE

Literature values for the equivalent width of the interstellar absorption line of Ca II K (3933 Å) are used to constrain a simple empirical model for the strength of this line as a function of distance from the galactic plane. The best-fit model has an integrated Ca II K equivalent width in the direction perpendicular to the galactic plane of approximately 200 mÅ and a "scale height" of approximately 1100 pc. Such a model is useful for estimating (and correcting for) the contribution of the interstellar Ca II K feature to the total observed Ca II K line strength in the spectra of metal-deficient stars in the galactic halo.