4 AGB ALMA images

All four stars show deviations from spherical symmetry. We find variations on a timescale of days to weeks, and for R Leo we directly measure an outward motion of the millimetre wavelength surface with a velocity of at least 10.6+/-1.4km/s. For all objects but W Hya we find that the temperature-radius and size-frequency relations require the existence of a (likely inhomogeneous) layer of enhanced opacity.

The ALMA observations provide a unique probe of the structure of the extended AGB atmosphere.We find highly variable structures of hotspots and likely convective cells. In the future, these observations can be directly compared to multi-dimensional chromosphere and atmosphere models that determine the temperature, density, velocity, and ionisation structure between the stellar photosphere and the dust formation region.

However, our results show that for the best interpretation, both very accurate flux calibration and near-simultaneous observations are essential.