Bipolar outflow on the asymptotic giant branch -: the case of IRC+10011

Near-infrared imaging of the asymptotic giant branch (AGB) star IRC + 10011 (= CIT3) reveals the presence of a bipolar structure within the central similar to0.1 arcsec of a spherical dusty wind. We show that the image asymmetries originate from similar to10(-4) M. of swept-up wind material in an elongated cocoon whose expansion is driven by bipolar jets. We perform detailed 2D radiative transfer calculations with the cocoon modelled as two cones extending to similar to1100 au within an opening angle of similar to30degrees, embedded in a wind with the standard r(-2) density profile. The cocoon expansion started less than or similar to200 yr ago, while the total lifetime of the circumstellar shell is similar to5500 yr. Similar bipolar expansion, at various stages of evolution, has been recently observed in a number of other AGB stars, culminating in jet breakout from the confining spherical wind. The bipolar outflow is triggered at a late stage in the evolution of AGB winds, and IRC + 10011 provides its earliest example thus far. These new developments enable us to identify the first instance of symmetry breaking in the evolution from AGB to planetary nebula.