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Astron. Astrophys. 354, L17-L20 (2000)

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Letter to the Editor

New PAH mode at 16.4 µ*

C. Moutou 1, L. Verstraete 2, A. Léger 2, K. Sellgren 3 and W. Schmidt 4

1 ESO, Alonso de Cordoba 3107, Santiago 19, Chile (cmoutou@eso.org)
2 IAS, CNRS, Université Paris Sud, 91405 Orsay, France (verstra@ias.fr, leger@ias.fr)
3 Astronomy Department , Ohio State University, 140 West 18th Avenue, Columbus OH 43210, USA (sellgren@astronomy.ohio-state.edu)
4 Institut für PAH-Forschung, Flurstrasse 17, 86926 Greifenberg, Germany

Received 12 October 1999 / Accepted 23 December 1999


The detection of a new 16.4 µm emission feature in the ISO-SWS spectra of NGC 7023, M17, and the Orion Bar is reported. Previous laboratory experiments measured a mode near this wavelength in spectra of PAHs (Polycyclic Aromatic Hydrocarbons), and so we suggest the new interstellar 16.4 µm feature could be assigned to low-frequency vibrations of PAHs. The best carrier candidates seem to be PAH molecules containing pentagonal rings.

Key words: ISM: abundances – ISM: dust, extinction – ISM: reflection nebulae

* based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: the United Kingdom, France, the Netherlands, Germany), and with the participation of ISAS and NASA.

Send offprint requests to: C. Moutou

© European Southern Observatory (ESO) 2000

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