High-resolution sodium absorption-line observations of the local interstellar medium

High-resolution observations of the sodium D1 and D2 interstellar absorption lines have been made toward 19 stars in the local ISM at distances ranging from 20 to 220 pc. A least-squares absorption line-fitting analysis is carried out on 10 of the stars that show detectable sodium. The velocity structure, velocity dispersions, and column densities of the various interstellar cloud components are derived. For the majority of stars, the best-fit dispersion parameter is about 2 km/s, corresponding to an upper limit for the kinetic temperature of the interstellar gas of about 5500 K. No sodium is detected toward stars with distances less than 42 pc, placing an upper limit 2.5 x 10 to the 18th/sq cm to the hydrogen column density in these lines of sight.