FURTHER HIGH-RESOLUTION NA-I OBSERVATIONS OF THE LOCAL INTERSTELLAR-MEDIUM

We present high-resolution absorption measurements (lambda/DELTA-lambda approximately 150,000) of the interstellar Na I D lines at 5890 angstrom observed toward 27 early-type stars in the local interstellar medium (LISM). These results are combined with other high-resolution sodium measurements to map the space distribution of neutral sodium column density for some 118 stars out to d = 200 pc. These measurements indicate an upper limit to the neutral sodium column density of log N(Na I) < 10.0 cm-2 can be inferred out to a distance of 50 pc in most directions in the LISM. Also, the rarefield region of the Local Bubble may extend beyond 60 pc in at least 35% of the directions sampled thus far. We show evidence for a ubiquitous, comoving vector for neutral Na I gas clouds in the LISM which is in a different direction to LISM vectors previously reported for more ionized local gas clouds. In addition, we have failed to detect any high-velocity (DELTA-V > 30 km s-1) components in these sodium absorption-line profiles. A comparison of the measured sodium columns with those of interstellar Ca II for a sample of 12 stars within 95 pc results in a ratio of Na I/Ca II < 0.5 for most stars. This value implies that there could be warm, neutral gas with T approximately 12,500 K beyond 50 pc in the LISM.