ORFEUS II echelle spectra: The scale height of interstellar O VI in the halo

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FUV high resolution spectra of 18 stars, particularly chosen to observe the interstellar medium (ISM), were obtained during the second ORFEUS-SPAS free flight space shuttle mission in December 1996. Among these were 6 objects with a distance to the galactic plane larger than 1 kpc, one SMC and 4 LMC stars. This selction of targets is part of the ORFEUS program to explore the galactic halo. As the most important tracer 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| = 3.5 x 10¹4 /cm² on the lines of sight to the 4 LMC stars. Assuming an exponential distribution of O VI we calculated a midplane density n(o) of 2.07 x 10-8 /cm³ and a scle height h(o) of 5.50 kpc. (Research supported in part by the DARA)