Plateau de bure observations of IRC+10216: high sensitivity maps of SiC₂, SiS, and CS

Abstract

We have obtained high angular resolution (∼ 3″), and high sensitivity maps of IRC+10216. SiC₂ is found both in a spherical shell and in the very central region, indicating it is formed both in the inner envelope close to the star, and in the outer shell. The molecules SiS and CS are mostly found in the inner parts of the envelope, but are still detectable in the outer region (r ∼ 15″) where the products of photochemistry are found. The maps show that IRC+10216 has a very clumpy envelope, with strong departures from spherical symmetry; an axis oriented NS-SW (P.A. 20°) can be seen in all maps. The radial brightness distribution of CS has secondary maxima, at the radius where the SiC₂ shell has its peak emission. A preliminary map shows CN in the same shell, but also in a still larger outer shell. Time variations in the mass loss rate, could be invoked to explain the multiple shell structure of this envelope.