Interstellar absorption in intercloud regions. II. Detection of the Na I lines

The weak interstellar absorption lines of Na I, Ca II, and H I formed in the intercloud medium toward seven nearly unreddened stars are analyzed. Together with the widths of the Na I and Ca II lines, the column-density ratios N (Na I)/N/sub H/ determine limits on the temperature of the absorbing gas, while the ratios N (Ca II)/N/sub H/ establish limits upon its calcium depletion. If n/sube/approx. =0.02 cm-3 in the absorbing regions, two of the seven temperatures are between 3200 K and 6000 K, while three others exceed lower limits ranging from 1400 K to 6500 K. The calcium depletions generally are less severe than in a typical cloud by at least an order of magnitude