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Colloquium: Unwinding the secrets of thermal pulses and sculpted winds in AGB stars with ALMA

Submitter: Matthias Maercker
Description: I will present ALMA Cycle 0 observations of the CO emission around the carbon AGB star R Sculptoris. The observations show the detached shell and circumstellar medium around this star in unprecedented detail.

The detached shell is formed due to the change in mass-lo ss rate and expansion velocity during a thermal pulse. Amazingly, the data also reveal a clear, and previously unobserved, spiral structure within and connected to the detached shell, indicating the likely presence of a companion star or high-mass planet. Combined with 3-dimensional hydrodynamical models, we for the first time set direct observational constraints on the changes in mass-loss rate and expansion velocity during and after a thermal pulse.

By modelling the stellar wind from a binary system, we show that the shape and density of the observed spiral depend on the changes in mass-loss rate and expansion velocity, as well as the duration of the pulse. The results imply a change in pulse to post-pulse mass-loss rate by a factor of 30, and a gradual decrease of the expansion velocity. We are thus able to uncover the fossil record of mass-loss on the AGB in unprecedented detail, ushering in a new paradigm in our understanding of this fundamental period of stellar evolution.
Copyright: Maercker
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