Synthesis of organic compounds in planetary nebulae and proto-planetary nebulae

Abstract

Recent millimeter-wave and infrared spectroscopic 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 the following proto-planetary nebula 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. Isotopic analysis of meteorites and interplanetary dust collected in the upper atmosphere have revealed the presence of pre-solar grains similar to those formed in evolved stars. This provides a direct link between star dust and the solar system and raises the possibility that the early solar system was chemically enriched by stellar ejecta. © 2006 American Institute of Physics.