When a low-mass star, near the end of its evolution, exhausts its hydrogen and helium fuel, its core contracts and evolves towards a white dwarf, while the outer layers are ejected and form an expanding shell of gas that soon becomes a planetary nebula. During the star's previous evolution, this gas has been enriched in heavy elements (carbon, oxygen, ...). Thus, they contribute to the enrichment of the interstellar gas that will form future stars, planets - and maybe organic life...

The enveloppe around the objet IRC+10216 has been observed with the 30m telescope (bottom spectrum) and the IRAM interferometer (maps below) at 3" resolution in the 3mm lines of various molecules. This high resolution allows to resolve small scale structures, barely larger than the solar system. The radial properties of the rings suggest the presence of mutiple shells.