The formation of polycyclic aromatic hydrocarbons in evolved
  circumstellar environments
  The formation of Polycyclic Aromatic Hydrocarbons in the circumstellar
outflows of evolved stars is reviewed, with an emphasis on carbon stars on the
Asymptotic Giant Branch. Evidence for PAHs present in their winds is provided
by meteoritic studies and recent observations of the Unidentified Infrared
bands. We detail the chemical processes leading to the closure of the first
aromatic ring as well as the growth mechanisms leading to amorphous carbon
grains. Existing studies on PAH formation in evolved stellar envelopes are
reviewed and new results for the modelling of the inner wind of the archetype
carbon star IRC+10216 are presented. Benzene, C6H6, forms close to the star, as
well as water, H2O, as a result of non-equilibrium chemistry induced by the
periodic passage of shocks. The growth process of aromatic rings may thus
resemble that active in sooting flames due to the presence of radicals like
hydroxyl, OH. Finally, we discuss possible formation processes for PAHs and
aromatic compounds in the hydrogen-rich R CrB star, V854 Cen, and their
implication for the carriers of the Red Emission and the Diffuse Interstellar
Bands.
