Poster abstract details

After very dense and slow winds erode the outer layer of an asymptotic giant branch (AGB) star down to a thin H-rich layer (~10-3MΘ,) the star becomes a post-AGB star and evolves at constant luminosity towards hotter temperatures. It may then become a planetary nebula (PN) with a planetary nebula nucleus (PNN) at its centre. During these phases, the thin H-rich surface layer of the star is eroded by winds. In particular, very fast and low density winds occur from the PNN which cause dramatic effects by dynamically interaction with the material that exists around the central stars from previous wind episodes. Stardust oxide and silicate grains that formed around AGB stars are recovered from meteorites. The origin of the “Group II grains” which show enrichments in 17O and depletions in 18O, is currently explained by invoking the occurrence of some kind of extra-mixing process in AGB stars who physical mechanism is a matter of debate. We propose an alternative explanation for their origin by suggesting that these grains may have originated from the winds of post-AGB stars and PNNs. By comparing our stellar model predictions to the composition observed in Group II grains we try to assess this hypothesis. We predict that these winds shows the signature of H-burning and that their composition is close to that of Group II grains. However, could dust grains actually form in these winds, and in large enough quantities? A possible site were dust formation may occur could be identified in the post-shock regions produced when fast winds from a PNN collide with the material surrounding the star, however, to our knowledge there are no theoretical or observational studies confirming or ruling out our hypothesis.