Imaging the circumstellar envelopes of AGB stars

¹ Groupe d'Astrophysique, UMR 5024 CNRS, Case CC72, Place Bataillon, 34095 Montpellier Cedex 5, France e-mail: mauron@graal.univ-montp2.fr
² Physics Department, New York University, 4 Washington Place, New York NY 10003, USA

Received: 21 December 2005
Accepted: 21 February 2006

Abstract

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   yr^-1, and they can be seen out to distances  kpc. The observations provide information on the mass loss history on time scales up to  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.