We have shown that the standard model of AFGL2688 cannot satisfactorily explain a large fraction of the observational data. Instead we have proposed a major revision of the model, which still involves a dense, dusty torus generating a bipolar flow, but with very different geometry to that employed in the standard model. We have shown how this can explain all the new observations we have presented, as well as all the existing data. Using a full radiative transfer code in axial symmetry we have constructed a model which provides an excellent fit to the SED and a reasonable fit to most of the images from the optical into the far-IR/mm regions. In our model the progenitor star must have left the AGB about two hundred years ago with a dramatic burst of equatorially concentrated mass-loss which ejected about 0.7M of its envelope over a period of a few hundred years. The results imply that the star must have had a fairly large initial mass, near the upper end of the AGB mass range. We suggest that the Cygnus Egg Nebula may develop into a high excitation PN with similar morphology to NGC7027.
© European Southern Observatory (ESO) 1997
Online publication: March 24, 1998