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Astron. Astrophys. 338, L1-L4 (1998)

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Letter to the Editor

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 and K. Werner 1

1 Institut für Astronomie und Astrophysik, Abteilung Astronomie, Universität Tübingen, Waldhäuserstrasse 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

Received 1 July 1998 / Accepted 9 August 1998


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 )[FORMULA] of [FORMULA] cm-2 on the lines of sight to the 4 LMC stars. Assuming an exponential distribution of O VI we calculated a midplane density [FORMULA] of [FORMULA] cm-3 and a scale height [FORMULA] of [FORMULA] kpc.

Key words: space Vehicles – ISM: general – ISM: structure – Galaxy: halo – Galaxy: structure – ultraviolet: ISM

Send offprint requests to: widmann@ait.physik.uni-tuebingen.de

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© European Southern Observatory (ESO) 1998

Online publication: September 8, 1998