Chemical Synthesis in the Circumstellar Environment: from carbon to aromatic molecules

Details Chemical Synthesis in the Circumstellar Environment: from carbon to aromatic molecules Chemical Synthesis in the Circumstellar Environment: from carbon to aromatic molecules

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aps..nws.c3001k&link_type=abstract

American Physical Society, Fourth Annual Meeting of the Northwest Section, abstract #C3.001

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It has been almost 50 years since the realization that most heavy elements are synthesized through direct or slow neutron capture nuclear reactions during the late stages of stellar evolution (Burbidge et al. 1957). For example, carbon is produced by triple-alpha reactions and is dredged up to the stellar surface in the asymptotic giant branch (AGB) phase. Because surface mass loss limits the growth of the carbon-oxygen core, carbon is never ignited under degenerate conditions and direct nuclear burning does not proceed beyond carbon for the majority (952000). Because of the low temperature ( 3000 K) environment, these freshly produced carbon atoms can react with oxygen and other elements to produce simple molecules (CO, CN, etc) in the atmosphere. More complicated molecules (up to 11 atoms) are synthesized in the circumstellar envelopes created by the mass outflow from the surface (Kwok 1987). Through millimeter-wave spectroscopy, the rotational transitions of over 50 molecules have been detected in the circumstellar envelopes of AGB stars. Recent observations with the Infrared Space Observatory have made possible the detection of vibration and bending modes of complex molecules. During the short (a few thousand years) transition phase from the AGB to planetary nebulae, complex molecules with aliphatic and aromatic structures have been detected. In this talk, I will review the spectroscopic evidence for the synthesis of large complex organic compounds in the circumstellar environment and discuss their implications on the chemical structure of the Galaxy. Burbidge, E. M., Burbidge, G.R., Fowler, W.A., Holye, F. 1957, Rev. Mod. Phys, 29, 547 Kwok, S. 1987, Physics Reports, 156, p. 111 Kwok, S. 2000, The Origin and Evolution of Planetary Nebulae, Cambridge University Press

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