Astronomy & Astrophysics

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Issue		A&A Volume 473, Number 3, October III 2007
Page(s)		L29 - L32
Section		Letters
DOI		10.1051/0004-6361:20078268

A&A 473, L29-L32 (2007)
DOI: 10.1051/0004-6361:20078268

Letter

A silicate disk in the heart of the Ant

O. Chesneau¹, F. Lykou², B. Balick³, E. Lagadec², M. Matsuura⁴, N. Smith⁵, A. Spang¹, S. Wolf⁶, and A. A. Zijlstra²

¹ Observatoire de la Côte d'Azur-CNRS-UMR 6203, Dept. Gemini, Avenue Copernic, 06130 Grasse, France
e-mail: olivier.chesneau@ob-azur.fr
² University of Manchester, School of Physics & Astronomy, PO Box 88, Manchester M60 1QD, UK
³ Astronomy Department, Box 351580, University of Washington, Seattle WA 98195, USA
⁴ National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
⁵ Astronomy Department, University of California, 601 Campbell Hall, Berkeley, CA 94720, USA
⁶ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

(Received 13 July 2007 / Accepted 23 August 2007)

Abstract
Aims.We aim at getting high spatial resolution information on the dusty core of bipolar planetary nebulae to directly constrain the shaping process.
Methods.We present observations of the dusty core of the extreme bipolar planetary nebula Menzel 3 (Mz 3, Hen 2-154, the Ant) taken with the mid-infrared interferometer MIDI/VLTI and the adaptive optics NACO/VLT.
Results.The core of Mz 3 is clearly resolved with MIDI in the interferometric mode, whereas it is unresolved from the $K{\rm s}$ to the N bands with single dish 8.2 m observations on a scale ranging from 60 to 250 mas. A striking dependence of the dust core size with the PA angle of the baselines is observed, that is highly suggestive of an edge-on disk whose major axis is perpendicular to the axis of the bipolar lobes. The MIDI spectrum and the visibilities of Mz 3 exhibit a clear signature of amorphous silicate, in contrast to the signatures of crystalline silicates detected in binary post-AGB systems, suggesting that the disk might be relatively young. We used radiative-transfer Monte Carlo simulations of a passive disk to constrain its geometrical and physical parameters. Its inclination (74° $\pm$ 3°) and position angle (5° $\pm$ 5°) are in accordance with the values derived from the study of the lobes. The inner radius is $9\pm 1$ AU and the disk is relatively flat. The dust mass stored in the disk, estimated as $1 \times 10^~M_{\odot}$ , represents only a small fraction of the dust mass found in the lobes and might be a kind of relic of an essentially polar ejection process.

Key words: planetary nebulae: individual: Mz 3 -- techniques: interferometric -- techniques: high angular resolution -- stars: circumstellar matter -- stars: mass-loss

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