The Synthesis of Organic Compounds in the Circumstellar Environment
Sun Kwok
Institute of Astronomy & Astrophysics, Academia Sinica, Taiwan
Résumé :
Recent ISO observations have found evidence
of rapid synthesis of complex organic molecules
in the late stages of stellar evolution.
The chemical synthesis begins with
the formation of acetylene, the first
building block of benzene, in carbon stars.
In a following proto-planetary nebulae stage,
emission features corresponding to stretching
and bending modes of aliphatic compounds are
detected. When these objects evolve
to become planetary nebulae, aromatic C-H and
C-C stretching and bending modes become strong.
These results show that complex carbonaceous
compounds can be produced in a circumstellar
environment over a period of only
a few thousand years.
Analysis of meteorites and interplanetary
dust collected in the upper atmospheres
have revealed the presence similar compounds,
raising the possibility that the early solar
system was chemically enriched by ejecta
from evolved stars.
In this talk, we will briefly describe
the origin and evolution of planetary nebulae,
the discovery of proto-planetary nebulae,
the discovery of the unidentified 21-micron
emission feature, and a possible scenario of
chemical evolution of organic material
in the circumstellar environment.
