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The Subaru Seminar is usually held in Room 104 of the Hilo Base Facility, adjacent to the main lobby. Everyone is welcome to attend. If you are interested in giving a seminar, please contact Subaru seminar organizers (Tomonori Usuda, Kumiko S. Usuda, Masayuki Akiyama) by email : (please change"_at" to @).

August 28, Tuesday at 2:00 pm

" Synthesis experiments of carbonaceous grain analogs and their infrared spectra "

Yuki Kimura (Ritsumeikan University)

I demonstrate a possible new formation route for fullerenes from CO gas by the Boudouard reaction in the circumstellar envelopes in post-asymptotic giant blanch (AGB) stars. The production of fullerenes will provide a unified explanation for the formation of TiC-core, graphitic-mantle spherules, which are extracted from primitive meteorites, and an origin of the 21-microns feature observed in post-AGB stars. Most of the carbon in the outflows of carbon-rich AGB stars is in the form of CO and C2H2. Carbonaceous materials such as polycyclic aromatic hydrocarbons and fullerenes are believed to form from C2H2 and its derivatives because CO is a very stable molecule. Therefore, no one ever considered CO gas as a carbon source. Here, I will demonstrate experimentally that large cage structure carbon particles can be produced from CO gas by the Boudouard reaction. Carbon particles were produced by resistive heating of a carbon rod in CO gas in the laboratory and were analyzed using high-resolution transmission electron microscope and infrared spectrometer. As a result, we found the first evidence of the presence of fullerenes around carbon-rich AGB stars. In the seminar, I will show a new formation process of core-mantle grains and an origin of 21-microns feature observed in carbon-rich post-AGB stars based on laboratory experiments.

" Laboratory studies on the formation of PAH clusters and their infrared spectra "

Midori Saito (Ritsumeikan University)

Polycyclic aromatic hydrocarbons (PAHs) have been considered most plausible candidates of the unidentified infrared bands observed from various astronomical objects in Galaxy and in extragalactic regions. Since it was believed that PAHs exist ubiquitously in the universe, the study of the life cycle of the PAHs leads to understand physical environments and chemical reaction process in various objects.
In order to elucidate the life cycle of the PAHs, I have performed experimental study on the formation of PAH clusters and measured their infrared spectra in the laboratory. Nanometer-sized PAH clusters were produced by evaporation of commercial powder in inert gas atmospheres. If the mechanisms of formation and growth of PAH clusters in this experiment were elucidated, it will be able to discuss the formation of PAH clusters in a gas out flow from evolved star. During the formation and growth of PAH clusters, PAH clusters may be undergone UV irradiation and plasma environments. Therefore, two other different experiments were performed: PAH clusters were produce in a plasma field and laboratory synthesized PAH clusters were exposed to UV radiation.

Seminars are also held at JAC, CFHT, and IfA.

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