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Analyzing astronomical observations with the NASA Ames PAH database

Published online by Cambridge University Press:  30 March 2011

C. Joblin ,
A.G.G.M. Tielens  and
J. Cami
J. Cami*
Affiliation:
Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 3K7, Canada SETI Institute - 189 Bernardo Ave., Suite 100 - Mountain View, CA 94043, USA

Abstract

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We use the NASA Ames Polycyclic Aromatic Hydrocarbon (PAH) infrared spectroscopic database to model infared emission of PAHs following absorption of a UV photon. We calculate emission spectra resulting from the full cooling cascade for each species in the database. Using a least squares approach, we can find out what PAH mixtures best reproduce a few typical astronomical observations representing the different classes of UIR spectra. We find that we can reproduce the observed UIR spectra in the wavelength range 6–14 μm, offering support for the hypothesis that the UIR bands are indeed due to vibrational modes of PAHs and related molecular species. Spectral decompositions of our best fit models confirm and reinforce several earlier results: (i) the 6.2 μm band requires a significant contribution of nitrogen-substituted PAHs (PANHs); (ii) the reported components and their variations in the 7.7 μm band are indicative of changes in the size distribution of the contributing molecules; (iii) there is a significant contribution of anions to the 7.7 μm band; (iv) the 11.2 μm band is due to large, neutral and pure PAHs; (v) the 11.0 μm band is due to large PAH cations.

Type
Research Article
Information
European Astronomical Society Publications Series , Volume 46: PAHs and the Universe: A Symposium to Celebrate the 25th Anniversary of the PAH Hypothesis , 2011 , pp. 117 - 122
Copyright
© EAS, EDP Sciences 2011

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