Final Activity Report Summary - VLBI OF AGB STARS (Very Long Baseline Interferometric astrometry of SiO masers around AGB stars to track the mass loss processes)
We designed a new method of calibration for very long baseline interferometry (VLBI) at mm wavelengths. This allowed the images to be astrometrically aligned, i.e. to put them on a common reference frame. We used this new method to image SiO masers around asymtopic giant branch (AGB) stars which were also Mira type variables. This informed us whether the source had emission from the different transitions in the same point in the sky. With this information we could work out which of the competing models for the excitation of the SiO maser emission was closer to reality. This information, in turn, allowed us to relate the observed emission to the underlying conditions. Whereas we could not previously say how much mass loss from these stars, which went on to form the beautiful proto-plantentary nebulea, was required to produce the observed maser emission this now became possible, even though our results made clear that both models needed updating.