Title: PAHs formation in the dense central torus of the O-rich pre-Planetary Nebula  Roberts 22.

Authors: Eric Lagadec, Lizette Guzman-Ramirez , Albert Zijlstra, Djamel Mekarnia, Greg Sloan, Krzysztof Gesicki

Abstract:  PAHs have been observed in the infrared spectra of some oxygen-rich post-AGB stars and Planetary Nebula. Such 
carbon-rich species are not expected to be present in an environment dominated by oxygen-rich chemistry. The post-AGB star 
Roberts 22 is one of the closest star known displaying this dual chemistry.
We used near-infrared adaptive optics imaging at the VLT/NACO and standard imaging with ISAAC/VLT, mid-infrared imaging 
with VLT/VISIR and integral field spectroscopy using SINFONI/VLT to map the PAHs distribution, as well as dust, molecular and 
ionised gas.
We show that the PAHs are present at the outer edge of the central torus. This is in agreement with models showing that the 
PAHs can be formed at the edge of dense torii following CO photodissociation. Long carbon-rich molecules can thus form in an 
oxygen-rich environment via the influence of a binary companion. This is a potential new source of PAHs for the interstellar 
medium.