Bispectrum Speckle Inter-Ferometry of the Carbon Star IRC+10216

The prototypical carbon Mira IRC+10 216 is an Asymptotic Giant Branch (AGB) star suffering from strong mass loss (several 10-5 M⊙/yr; Loup et al. 1993) which has led to an almost complete obscuration of the star by dust. Due to the high mass-loss rate, long period of P = 649 d and carbon-rich chemistry of the dust-shell, IRC +10 216 is obviously in a very advanced stage of its AGB evolution. High-resolution near-infrared imaging of IRC +10 216 has revealed that on sub-arcsecond scales (100 mas) its dust shell is clumpy, bipolar, and changing on a time scale of only ~1 yr (Weigelt et al. 1997, 1998, Haniff & Buscher 1998, Osterbart et al. 2000, Tuthill et al. 2000). Since most dust shells around AGB stars are known to be spherically symmetric, whereas most proto-planetary nebulae (PPN) show an axisymmetric geometry (Olofsson 1996) it appears likely that IRC+10 216 has already entered the transition phase to the PPN stage