The evolution of the planetary nebula NGC 6826

The density and mass profiles of the planetary nebula NGC 6826 are studied. New CCD images are used to deconvolve the density from the emission measure in Ha, assuming that the planetary nebula is spherically symmetric. For an assumed distance of 1.54 kpc the mass of the inner region r<13 arcsec is ∼0.15 M_⊙ and that the entire visible planetary nebula is 0.54 M_⊙. The possible formation of the dense shell at the edge of the nebula as a result of interaction with the ISM is discussed. The formation of the spherical outer halo together with an elliptical inner region can be explained by a low mass companion to the progenitor of NGC 6826 that was evaporated or collided with the central star.