Synthesis of Complex Organics in the Late Stages of Stellar Evolution

Speaker: 
Sun Kwok (The University of Hong Kong)
Event Date and Time: 
Fri, 2012-02-17 15:00 - 16:15
Location: 
Hennings 318
Local Contact: 
Jaymie Matthews
Intended Audience: 
Graduate
The last phase of stellar evolution from the asymptotic giant branch (AGB) to proto-planetary nebulae, to planetary nebulae represents the most active period of synthesis of organic compounds in a star’s life. Both inorganic and organic molecules and solids are found to form in the circumstellar envelopes created by stellar winds. Over 60 gas-phase molecules, including rings, radicals, and molecular ions have been identified by millimeter-wave and infrared spectroscopic observations through their rotational and vibrational transitions. Infrared spectroscopic observations of emissions from the stretching and bending modes of aliphatic and aromatic compounds have revealed a continuous synthesis of organic material from the end of the AGB to proto-planetary nebulae, to planetary nebulae. These results show that complex carbonaceous compounds can be produced in a circumstellar environment over a period of only a few thousand years. In contrast to the hypothesis of polycyclic aromatic hydrocarbon molecules which has been popular in the astronomical literature in the past 20 years, we find that the spectroscopic signatures of the stellar organics are more consistent with nano-particles of a mixed aromatic and aliaphatic structure. These structures are very similar to those of the insoluble organic matter found in meteorites, suggesting that there is a link between star dust and the solar system. This raises the possibility that the early solar system was chemically enriched by stellar ejecta with the potential of influencing the origin of life on Earth.
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