Résumé
The formation of polycyclic aromatic hydrocarbon (PAH) molecules is studied in the inner envelope of a typical carbon-rich AGB star. The deep envelope is formed of layers of gas that experience the passage of strong periodic shocks forming close to the stellar photosphere. The parcels of gas then follow quasi-ballistic trajectories which are characterized by high gas densities. A chemical scheme based on combustion chemistry is applied to shocked layers of gas, and a PAH formation yield is calculated. PAHs up to coronene (C24H12) survive shocks with strengths of ~ 10 km s-1, and they accumulate in the gas parcel over several stellar pulsations. This result illustrates that any C-rich AGB star can nucleate dust precursors in its envelope.