Thursday

Massive stars eject the bulk of their material towards the ends of their lives, contributing several - or many - solar masses of molecules and dust into the environment during the Red Supergiant phase. We do not really understand how matter is ejected from the stellar surface, nor how it travels the first few stellar radii until dust is well-formed and radiation pressure accelerates the wind, nor whether any cool material can survive into the ISM. With a radius typically comparable to the orbit of Jupiter, the stellar surface is very inhomogenous and interferometric imaging suggests the presence of starspots on a similar scale to recent models of convection cells. Allowing for expansion in the outflow, this is consistent with the sizes of water maser clumps. Detailed images in 5 transitions, spanning exitation states from 200 to 2600 K, are already available thanks to ALMA, MERLIN and other radio interferometers. Multi-level maser observations, combined with new models, allow us to reconstruct physical conditions as well as kinematics. Thus, we can constrain the temperature, number density, water abundance and other parameters in an order of magnitude finer detail than thermal lines, and investigate the differences between clumps and their surroundings, and their evolution in the wind.