Astronomy & Astrophysics

Issue		A&A Volume 452, Number 1, June II 2006
Page(s)		257 - 268
Section		Interstellar and circumstellar matter
DOI		10.1051/0004-6361:20054739

A&A 452, 257-268 (2006)
DOI: 10.1051/0004-6361:20054739

Imaging the circumstellar envelopes of AGB stars

N. Mauron¹ and P. J. Huggins²

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 ${\ga} 5\times 10^$ $M_{\odot}$ 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.

Key words: stars: AGB and post-AGB - stars: mass-loss - stars: circumstellar matter -- stars: late-type

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