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

摘要

We present new Herschel/PACS images at 70, 100, and 160 micron of thewell-known, nearby, carbon-rich asymptotic giant branch star IRC+10216revealing multiple dust shells in its circumstellar envelope. For the firsttime, dust shells (or arcs) are detected until 320 arcsec. The almost sphericalshells are non-concentric and have an angular extent between 40 deg and 200deg. The shells have a typical width of 5 arcsec - 8 arcsec, and the shellseparation varies in the range of 10 arcsec - 35 arcsec, corresponding to500-1700 yr. Local density variations within one arc are visible. Theshell/intershell density contrast is typically 4, and the arcs contain some 50%more dust mass than the smooth envelope. The observed (nested) arcs record themass-loss history over the past 16 000 yr, but Rayleigh-Taylor andKelvin-Helmholtz instabilities in the turbulent astropause and astrosheath willerase any signature of the mass-loss history for at least the first 200 000 yrof mass loss. Accounting for the bowshock structure, the envelope mass aroundIRC+10216 contains >2Msun of gas and dust mass. It is argued that the origin ofthe shells is related to non-isotropic mass-loss events and clumpy dustformation.