Evolution of the mira-type star S Orionis

The three images show different epochs in the evolution of the red star S Orionis. The red and blue spots result from the radio emission of the maser shell. The radio observation is overlapped to the simultaneous infrared detection: indeed the red disc indicates the stellar surface and the molecular layers, while the green shades represent the location of the dust shell. The first two images are obtained close to the stellar minimum luminosity, when most of the dust is produced. The third image is taken just after the visual maximum, when the dust shell already expanded. The study was made using ESO's VLTI on Cerro Paranal and the VLBA facility operated by NRAO.