Molecular complexity in the circumstellar envelope of the O-rich evolved star VY CMa

Envelopes around evolved stars are factories of complex molecules (neutrals, anions and cations) and one of the main sites for dust formation. Most chemical studies have focused on Crich envelopes, in particular on IRC+10216.Recent observations of metal bearing species and hydroxides inOrich shells suggest that the chemistry in these objects can beas richer as in Crich circumstellar envelopes. We propose toperform a complete line survey of the prominent Orich star VY CMa with HIFI.This study will provide, in addition to all lines of CO, H2O, HCN, SiO, SO2,a complete inventory of the molecular gas in Orich evolved stars.The comparison with the line survey of IRC+10216 (already carried out with HIFI/Herschel)will permit to distingush the different chemical processes in these objects and the subtlerole of the C/O abundance ratio in the molecular composition of the gas at differentdistances from the central star.We will use our radiative transfer and chemistry models to reproducethe observed spectra and to derive molecular abundances. The data willalso allow a better understanding of the physical structure of the envelope. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]