Thesis Topic: Imaging and Monitoring of Cool Evolved Stars: Constraining Effects of Convection, Pulsation, and Binarity


Thesis Supervisor: Markus Wittkowski


Mass-loss from cool evolved stars is an important ingredient of the cosmic matter cycle, enriching the Universe with newly formed elements and dust. It is also important for the further stellar evolution of these stars toward planetary nebulae and core-collapse supernovae. For low-and-intermediate-mass asymptotic giant branch (AGB) stars, it has been shown that pulsation and convection lead to strongly extended molecular atmospheres, where the temperature is cool enough for dust to form. For massive red supergiants (RSGs), however, current dynamic model atmospheres, based on pulsation and convection alone, cannot explain observed atmospheric extensions by far. Moreover, close companions may have a considerable effect on the mass-loss process of the primary.

This PhD project includes interferometric monitoring and imaging of both AGB and RSG stars, with and without known companions. We will use the PIONIER, GRAVITY, and MATISSE instruments of the Very Large Telescope Interferometer (VLTI), and possibly ALMA observations of SiO emission in collaboration with E. Humphreys (JAO, Chile). Data are partly already obtained and partly scheduled to be obtained. Further data will be proposed for together with the student. The data will be compared to latest 1D and 3D dynamic models of the mass-loss process in collaboration with the developers (A. Chiavassa, Nice; S. Hoefner, Uppsala).