Optical interstellar lines in dark clouds. II. K i and ultraviolet sodium lines

Abstract

New observations of the K i and ultraviolet Na i interstellar lines are presented for some stars embedded in dense clouds and for a few supergiants. The new observations of weak lines, which are essentially unaffected by the adopted velocity distribution for the interstellar material, support the conclusions previously obtained from the interstellar D-lines of Na i and H- and K-lines of Ca ii The new data, when combined with a discussion of the ionization equilibrium, indicate no or moderate depletions at the edges of clouds, but some depletions in the central regions.