The circumbinary disc around the J-type C-star IRAS 18006-3213^*

¹ Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium e-mail: pieter.deroo@ster.kuleuven.be
² Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

Received: 6 October 2006
Accepted: 6 March 2007

Abstract

Context.In the generally accepted, but poorly documented model, silicate J-type C-stars are binary objects for which the silicate emission originates from a circumbinary or a circumcompanion disc.

Aims.We aim at testing this hypothesis by a thorough spectral and spatial observational study of one object: IRAS 18006-3213.

Methods.We obtained, analysed and modeled high spatial resolution interferometric VLTI/MIDI observations on multiple baselines ranging from 45 m to 100 m.

Results.All observations resolved the object and show the very compact nature of the N-band emission (~30 mas). In addition, the highest spatial resolution data show a significant differential phase jump around 8.3 μm. This demonstrates the asymmetric nature of the N-band emission. Moreover, the single telescope N-band spectrum shows the signature of highly processed silicate grains. These data are used to confirm the model on silicate J-type C-stars for IRAS 18006-3213. We show that the most favourable model of the dust geometry is a stable circumbinary disc around the system, seen under an intermediate inclination.

Conclusions.The data presented on the silicate J-type C-star IRAS 18006-3213 provide evidence that the oxygen rich dust is trapped in a circumbinary disc. The formation of this disc is probably linked to the binary nature of the central star.