Astron. Astrophys. 359, 1111-1116 (2000)

ORFEUS II echelle spectra: H₂ measurements in the Magellanic Clouds ^*

Ph. Richter <sup>1,2

1</sup> Sternwarte, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
² Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706, USA

Received 15 November 1999 / Accepted 27 April 2000

Abstract

More than 20 years after the Copernicus satellite, ORFEUS allows the investigation of molecular hydrogen (H₂) in the diffuse interstellar medium by way of FUV absorption spectroscopy once again. This time, targets in the Magellanic Clouds were also observed, allowing the first investigation of cold H₂ in a metal-poor environment outside the Milky Way disk. This paper presents new H₂ measurements in LMC gas along the lines of sight toward HD 269698 (Sk -67 166), HD 269546 (Sk -68 82) and HD 36402 (Sk -67 104) and summarizes the ORFEUS H₂ measurements in the the Magellanic Clouds. For seven lines of sight we investigate correlations between H I , H, and compare the results with H₂ observations in the Milky Way disk. We find that the abundance of H₂ is low in comparison to the total gas quantity and speculate that the fraction of hydrogen in molecular form is limited by the lower dust content of the Magellanic Clouds.

Key words: space vehicles galaxies: ISM galaxies: Magellanic Clouds ultraviolet: ISM

* Data partly obtained under the DARA guest observing program in the ORFEUS II Mission

Send offprint requests to: Ph. Richter (richter@astro.wisc.edu)

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Contents

• 1. Introduction
• 2. Observations
• 3. Data analysis
• 4. ORFEUS H₂ measurements
  • 4.1. HD 269698
  • 4.2. HD 269546
  • 4.3. HD 36402
• 5. H I measurements
• 6. Colour excess
• 7. Discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000
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