Invited Talk

Unidentified Infrared Emission Features

Christine Joblin (IRAP, University of Toulouse, CNRS)

When referring to unidentified infrared emission features, one has in mind the series of aromatic IR bands (AIBs) at 3.3, 6.2, 7.7, 8.6, 11.3 and 12.7 microns that are observed in emission in many environments where UV photons irradiate interstellar matter. The best carriers for the AIBs are polycyclic aromatic hydrocarbon (PAH) molecules. Despite the recent identification of C60 that supports the presence of large aromatic molecules in space, there has been no identification of a single PAH in space. One has therefore to progress in our understanding on how these species are formed, most likely in the envelopes of evolved carbonaceous stars, and their further processing in the interstellar medium. Various studies have been performed along this line and have shown the appearance of AIBs in evolved stars at the protoplanetary stage as well as the evolution of the AIB spectrum at the surface of photodissociation regions (PDRs). All the studies have emphasized the need for studying the link between the molecular aromatic species constituting the AIB carriers, aliphatic material and very small carbonaceous grains. Other unidentified infrared emission features such as the 6.9, the 21 and possibly the 30 micron bands have to be considered to build a plausible evolutionary scenario. I will review our current knowledge on this subject.

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