Olivier Berné (IRAP) Thursday November 7th - 11am Seminar Room - IRAM
The mid-infrared (5-15 um) spectrum of most astronomical objects is characterized by broad spectral bands observed in emission. The "PAH model", introduced in the mid 80’s by Leger & Puget and Allamandola et al., postulates that these bands are due to the fluorescence of large carbonaceous molecules. At the same time, while trying to reproduce the physical and chemical conditions present in the envelopes of evolved stars, Harold Kroto and his collaborators synthesized serendipitously a new carbonaceous macromolecule, containing exactly 60 carbon atoms organized in a cage-like structure similar to a soccer ball : buckminsterfullerene (C60). For this discovery which basically launched the field of nano-technologies, they received the Nobel prize in 1996. However, on the astronomical side, problems still remained : no specific carbonaceous macromolecule could be identified spectrocopically to be present in space therefore precluding a full validation of the PAH model. This was until the identification, in 2010, of C60 in an evolved star and in the interstellar medium, respectively by Cami et al. and Sellgren et al. Although this represented a significant step forward in the field, it could not be proven by these authors that, as proposed in the PAH model, C60 was fluorescing. In addition, the presence of C60 in space reopened an un-answered question : how is this symmetric "magic" molecule formed ? In this seminar, I will present new results which provide possible answers to these questions. In addition, I will discuss on the possibility to identify other carbonaceous macromolecules in space though their far-infrared emission. I will finish by summarizing the arguments which support the PAH model and describe how it can be used to probe the universe, at low and high redshifts.
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