Astron. Astrophys. 331, 742-748 (1998)

Detection of UIR bands in an isolated local interstellar cirrus cloud ^*

D. Lemke ¹, K. Mattila ², K. Lehtinen ², R.J. Laureijs ⁴, T. Liljeström ², A. Léger ³ and U. Herbstmeier <sup>1

1</sup> Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
² Observatory, P.O. Box 14, FIN-00014 University of Helsinki, Finland
³ Institut d'Astrophysique Spatiale, C.N.R.S., Université Paris XI, France
⁴ ISO Science Operations Team, ESA - Villafranca, Villafranca del Castillo, Aptdo 50727, E-28080 Madrid, Spain

Received 12 June 1997 / Accepted 3 November 1997

Abstract

The unidentified infrared (UIR) emission bands at 7.7 and 11.3 µm have been detected in the emission of an isolated cirrus cloud externally heated by the typical interstellar radiation field (ISRF) of the solar neighbourhood. For the observations we used ISOPHOT, the photometer aboard ISO. The detected UIR bands have absolute intensities 1/1000th of the values typically observed in planetary and reflection nebulae. The intensity ratio 11.3 to 7.7 µm is at the higher end of the range observed for reflection nebulae, planetaries, HII regions, or for the diffuse emission of the inner Galaxy. An enhanced emission level is observed also in the bands 6 - 9 µm and 12 - 14 µm, suggesting the presence of the 6.2, 8.6 and 12.7 µm UIR bands. At 10 and 16 µm continuum emission has been detected which must be due to very small grains. The observations presented give further evidence that the UIR features seem to be ubiquitous throughout the galaxy. This is in support of the PAHs as carriers of the features and, moreover, as key agents in transforming the stellar UV into infrared radiation.

Key words: dust, extinction infrared: ISM: lines and bands Galaxy: general

* Based on observations made with ISO, an ESA project with instruments funded by ESA member states (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA

Send offprint requests to: D. Lemke (email:lemke@mpia-hd.mpg.de)

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and reductions
• 3. Results
• 4. Discussion
  • 4.1. PAH energy budget
  • 4.2. Band ratios and PAH properties
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: February 16, 1998
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