Imaging the circumstellar envelopes of AGB stars

Aims.We report the results of an exploratory program to image the extended circumstellar envelopes of asymptotic giant branch (AGB) stars in dust-scattered galactic light. The goal is to characterize the morphology of the envelopes as a probe of the mass-loss process. Methods.The observations consist of short exposures with the VLT and longer exposures with 1–2 m telescopes, augmented with archival images from the Hubble Space Telescope. Results.We observed 12 AGB stars and detected the circumstellar envelopes in 7. The detected envelopes have mass loss rates ${\ga} 5\times 10^{-6}$ $M_{\odot}$ yr-1, and they can be seen out to distances ${\ga} 1$ kpc. The observations provide information on the mass loss history on time scales up to ${\sim} 10\,000$ yr. For the five AGB envelopes in which the circumstellar geometry is well determined by scattered light observations, all except one (OH348.2-19.7) show deviations from spherical symmetry. Two (IRC+10216 and IRC+10011) show roughly spherical envelopes at large radii but asymmetry or bipolarity close to the star; one (AFGL 2514) shows an extended, elliptical envelope, and one (AFGL 3068) shows a spiral pattern. The non-spherical structures are all consistent with the effects of binary interactions. Conclusions.Our observations are in accord with a scenario in which binary companions play a role in shaping planetary nebulae, and show that the circumstellar gas is already partly shaped on the AGB, before evolution to the proto-planetary nebula phase.