ORFEUS II echelle spectra : H_2 measurements in the Magellanic Clouds

Philipp Richter

Published 2000-05-12Version 1

More than 20 years after the Copernicus satellite, ORFEUS allows the investigation of molecular hydrogen (H_2) 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 H_2 in a metal-poor environment outside the Milky Way disk. This paper presents new H_2 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 H_2 measurements in the the Magellanic Clouds. For seven lines of sight we investigate correlations between N(H I), N(H_2), E(B-V) and compare the results with H_2 observations in the Milky Way disk. We find that the abundance of H_2 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.