In the carbon cycle of the Universe, a major role is played by Polycyclic Aromatic Hydrocarbons (PAHs) and related organic compounds. PAHs are thought to form in the outflows of carbon-rich evolved stars; this material is then injected into the interstellar medium. Along the way, these species are processed and modified. A good understanding of this organic reservoir and the processing involved represents a major contribution to our knowledge of the evolution of carbon in the Universe.<br/> <br/>The evolution from pristine to (fully) processed PAHs can in principle be traced observationally by their strong and omnipresent infrared signature. Nevertheless, many aspects of the formation of PAHs, their evolution, and their interrelationship/interaction with other carbonaceous species remain unclear.<br/><br/>In this talk, I will present an overview of the large amount of astronomical observations of PAHs in evolved stars. I will show how targeted studies combined with dedicated spectroscopic databases can yield important clues to understanding PAH evolution. I will give an overview of what characteristics we have been able to unravel, and of the remaining problems.

Observations of organic molecules in carbon-rich proto-planetary nebulae and planetary nebulae

249th National Meeting (2015)

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