Animation of binary system developing a spiral structure

Supplementary Information of the paper "Unexpectedly large mass loss during the thermal pulse cycle of the red giant star R Sculptoris," authored by M. Maercker, S. Mohamed, W. H. T. Vlemmings, S. Ramstedt, M. A. T. Groenewegen, E. Humphreys, F. Kerschbaum, M. Lindqvist, H. Olofsson, C. Paladini, M. Wittkowski, I. de Gregorio-Monsalvo & L.-A. Nyman, published in Nature 490, 232--234 (11 October 2012) DOI: http://dx.doi.org/10.1038/nature11511 Abstract: "The asymptotic-giant-branch star R Sculptoris is surrounded by a detached shell of dust and gas. The shell originates from a thermal pulse during which the star underwent a brief period of increased mass loss. It has hitherto been impossible to constrain observationally the timescales and mass-loss properties during and after a thermal pulse—parameters that determine the lifetime of the asymptotic giant branch and the amount of elements returned by the star. Here we report observations of CO emission from the circumstellar envelope and shell around R Sculptoris with an angular resolution of 1.3″. What was previously thought to be only a thin, spherical shell with a clumpy structure is revealed to also contain a spiral structure. Spiral structures associated with circumstellar envelopes have been previously seen, leading to the conclusion that the systems must be binaries. Combining the observational data with hydrodynamic simulations, we conclude that R Sculptoris is a binary system that underwent a thermal pulse about 1,800 years ago, lasting approximately 200 years. About 3 × 10^−3 solar masses of material were ejected at a velocity of 14.3 km/s and at a rate around 30 times higher than the pre-pulse mass-loss rate. This shows that about three times more mass was returned to the interstellar medium during and immediately after the pulse than previously thought." "In the animation we model a binary system with a primary mass of 1.6 M, a companion mass of 0.25 M, and a separation of 60 AU. The shaping of the wind into a spiral structure is clearly visible. At t = 0 years the AGB star undergoes a thermal pulse, forming an expanding detached shell. The post-pulse mass-loss continues to form a spiral, connecting the detached shell with the central star. At t ≈ 2,000 years the system has formed a detached shell and spiral structure as observed in the ALMA observations. See Supplementary Information PDF for full video legend."