The circumbinary disc around the J-type C-star <ASTROBJ>IRAS 18006-3213</ASTROBJ>

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: <ASTROBJ>IRAS 18006-3213</ASTROBJ>. 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 mum. 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 <ASTROBJ>IRAS 18006-3213</ASTROBJ>. 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 <ASTROBJ>IRAS 18006-3213</ASTROBJ> 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. Based on observations collected at the European Southern Observatory, Chile. Program ID: 073.D-610(A).