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Astron. Astrophys. 338, L9-L12 (1998)


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Letter to the Editor

ORFEUS II echelle spectra: Detection of H2 absorption in SMC gas

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

1 Sternwarte, Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
2 Institut für Astronomie und Astrophysik, Abteilung Astronomie, Universität Tübingen, Waldhäuserstrasse 64, D-72076 Tübingen, 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 2 July 1998 / Accepted 9 August 1998

Abstract

We present a study of H2 in the SMC gas, based on Far UV spectroscopy in the line of sight to the SMC star HD 5980. 17 absorption lines from the Lyman band have been analysed. Our line of sight crosses two clouds within the SMC. We detect a cool molecular component near +120 km s-1, where the H2 from the lowest 3 rotational states ([FORMULA]) is found. For this cloud we derive an excitation temperature of [FORMULA] 70 K, probably the kinetic temperature of the gas. Another SMC component is visible at +160 km s-1. Here we find unblended H2 absorption lines from levels [FORMULA]. For this component we obtain an equivalent excitation temperature of [FORMULA] 2350 K and conclude that this cloud must be highly excited by strong UV radiation from its energetic environment.

Key words: space vehicles .- ISM: molecules – galaxies: ISM – Magellanic Clouds: SMC – stars: individual: HD 5980 – ultraviolet: ISM

Send offprint requests to: prichter@astro.uni-bonn.de

© European Southern Observatory (ESO) 1998

Online publication: September 8, 1998

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