Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC+10216 using Herschel/PACS

We present new Herschel/PACS images at 70, 100, and 160 mu m of the well-known, nearby, carbon-rich asymptotic giant branch star IRC + 10216 revealing multiple dust shells in its circumstellar envelope. For the first time, dust shells (or arcs) are detected until 320 ''. The almost spherical shells are non-concentric and have an angular extent between similar to 40 degrees and similar to 200 degrees. The shells have a typical width of 5 ''-8 '' and the shell separation varies in the range of similar to 10 ''-35 '',corresponding to similar to 500-1 700 yr. Local density variations within one arc are visible. The shell/intershell density contrast is typically similar to 4, and the arcs contain some 50% more dust mass than the smooth envelope. The observed (nested) arcs record the mass-loss history over the past 16 000 yr, but Rayleigh-Taylor and Kelvin-Helmholtz instabilities in the turbulent astropause and astrosheath will erase any signature of the mass-loss history for at least the first 200 000 yr of mass loss. Accounting for the bowshock structure, the envelope mass around IRC+10216 contains >2 M-circle dot of gas and dust mass. It is argued that the origin of the shells is related to non-isotropic mass-loss events and clumpy dust formation.