Institut für Astronomie und Astrophysik

Abteilung Astronomie

Preprint F/98

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

H. Widmann(1), K. S. de Boer(2), P. Richter(2), G. Krämer(1), I. Appenzeller(3), J. Barnstedt(1), M. Gölz(1), M. Grewing(4), W. Gringel(1), H. Mandel(3), K. Werner(1)

(1)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2)Sternwarte, Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
(3)Landessternwarte Heidelberg, Königstuhl, D-69117 Heidelberg, Germany
(4)Institut de Radio Astronomie Millimétrique (IRAM), 300 Rue de la Piscine, F-38406 Saint Martin d'Hères, France

1998, Astronomy & Astrophysics, 338, L9

Abstract. 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)*sin|b| of ~3.5*10^{14} cm^-2 on the lines of sight to the 4 LMC stars. Assuming an exponential distribution of O VI we calculated a midplane density n_0 of 2.07(+0.26,-0.24)*10^{-8} cm^-3 and a scale height h_0 of 5.50(+2.37,-2.09) kpc.

Key words: Space Vehicles - ISM: general - ISM: structure - Galaxy: halo - Galaxy: structure - Ultraviolet: ISM

Paper (57k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de) Last updated 25-Sep-1998