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

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 mis- sion 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 pro- gram to explore the galactic halo. As the most important tracer of the hot gas we analyzed the stronger component of the impor- tant Ovi doublet in all our ISM spectra. We found an average N (Ovi)sin jbj of 3:5 10 14 cm 2 on the lines of sight to the 4 LMC stars. Assuming an exponential distribution of Ovi we calculated a midplane density n0 of 2:07 +0:26 0:24 10 8 cm 3