Discovery of multiple molecular shells in the outer envelope of IRC+10216

We present (CO)-C-12 J = 1 --> 0 maps of the extended envelope of IRC +10216 made by combining BIMA millimeter array and NRAO 12 m telescope observations. CO emission was detected beyond the radius of 140", which traces the history of mass loss for the past similar to7000 yr. We discover superposed on the CO envelope clumpy arcs of enhanced emission, circumscribing the star, at multiple radii ranging from about 26" to 120". The arcs are found to be coherent across a range of velocities, thus forming sections of multiple shells that are participating in the circumstellar expansion. The intershell timescales range from 1300 to 2900 yr, which are roughly consistent with simulations where wind modulations from a single thermal pulse event can lead to the formation of multiple shells. The multiple enhanced shells within the continuous envelope of IRC +10216 may be the high mass-loss rate counterpart to the detached shells detected around several low mass-loss rate carbon stars, such as TT Cyg.