KINEMATICAL STRUCTURE OF THE LOCAL INTERSTELLAR-MEDIUM - THE GALACTIC-CENTER HEMISPHERE

A survey of interstellar Na I D-1 and D-2 absorption features found in the spectra of 31 early-type stars in the first and fourth Galactic q uadrants reveals a new picture of the large-scale kinematics of inters tellar gas in the vicinity of the Sun. While absorption features found in the spectra of stars in the fourth Galactic quadrant show the gas expanding from stars in the Scorpio-Centaurus OB association, stars in the first Galactic quadrant, in the range of distances covered by thi s survey (74-312 pc from the Sun), show interstellar gas falling towar d the Galactic plane with a bulk motion whose component parallel to th at plane is directed toward the Scorpio-Centaurus association. This pi cture differs completely from generally accepted models in which the n earby interstellar gas flows away from the Scorpio-Centaurus associati on toward the Galactic anticenter. Evidence for the presence of an exp anding shell-like feature that is reaching the solar system is present ed.