DETECTION OF HOT GAS IN THE INTERSTELLAR-MEDIUM

We present data on the C IV, Si IV, and N V absorption lines in eight disk stars observed by HST (Hubble Space Telescope) with the GHRS (God dard High Resolution Spectrograph) at intermediate resolution. C IV an d Si IV absorption lines are detected in seven target stars, while N V lines are detected in four distant stars and one nearby star. By fitt ing these absorption lines, we find a strong linear correlation betwee n the column densities of the ions and distance. The average column de nsity ratios of C IV to Si IV and C IV to N V are 4.7 and 3.0, which r oughly match the result of IUE surveys. A correlation of the line widt hs of C IV and Si IV leads to the suggestion that the Si IV and most o f the C IV originate in the same place. The lower ionization absorptio n lines, Si III (1206.5 Angstrom), Si II (1260.4 A), S II (1259.4 Angs trom), and N I(1199.6 Angstrom), are also measured. Effective widths o f high- and low-ionization absorption lines are also correlated with e ach other. Such a correlation may indicate a real physical connection between hot and cold gas if the filling factor of the absorber is smal l and the number of such absorption regions in the line of sight is sm all. Physical properties of the hot gas-producing C IV and Si IV lines are also discussed. We suggest that there are about three such region s per kiloparsec.