ORFEUS-II-ECHELLE SPECTRA - THE SCALE HEIGHT OF INTERSTELLAR-O-VI IN THE HALO

FUV high resolution spectra of 18 stars, particularly chosen to observ e the interstellar medium (ISM), were obtained during the second ORFEU S-SPAS free flight space shuttle mission in December 1996. Among these were 6 objects with a distance to the galactic plane larger than 1 kp c, one SMC and 4 LMC stars. This selction of targets is part of the OR FEUS program to explore the galactic halo. As the most important trace r of the hot gas we analyzed the stronger component of the important O VI doublet in all our ISM spectra. We found an average N(O VI) X sin \b\ of similar to 3.5 x 10(14) cm(-2) on the lines of sight to the 4 L MC stars. Assuming an exponential distribution of O VI we calculated a midplane density n(0) of 2.07(-0.24)(+0.26) x 10(-8) cm(-3) and a sca le height ho of 5.50(-2.09)(+2.37) kpc.