Interstellar Na I and Ca II absorption in intercloud regions

The weak interstellar absorption lines of Na i, Ca ii, and H i formed in the intercloud medium toward eight nearly unreddened stars are analyzed. Compared with the corresponding column densities within a standard cloud, the N (Na i)/N/sub H/ ratio is smaller by a factor probably in excess of 17, while the N (Ca ii)/N/sub H/ ratio is about normal. These results imply that the local intercloud medium extensively contains low-density H i regions in which the temperature Tapproximately-greater-than2500 K and the depletion of calcium is less severe than in the clouds by a factor of 20