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Synthesis of Organic Compounds in Planetary Nebulae and Proto-Planetary Nebulae

AIP Conference Proceedings, 2006
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.
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A New Planetary Nebula

Symposium - International Astronomical Union, 1989
The object (α1950 = 18h04m.3; δ1950 = −8o56!4) was discovered in a 103a-E+RG 1 objective prism plate taken with the 92/67-cm Schmidt telescope of the Astrophysical Observatory of Asiago (Italy). It presents only the Hα emission and no stellar continuum; following Kohoutek (1965, 1969, 1972) it is a bona fide planetary nebula.
M. Turatto, F. Sabbadin, E. Capellaro
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Evolution of planetary nebulae

The Astronomy and Astrophysics Review, 1992
A second argument in this direction was given by several astronomers in the 1950's. It had long been known from the double peaked emission lines observed in the nebulae, that they were expanding. The velocity of expansion is on the average 15 to 20 km s -t, with only exceptional cases differing by more than a factor 2 from this value.
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Extreme 13C,15N and 17O isotopic enrichment in the young planetary nebula K4-47