Resolving the extended atmospheres of AGB stars

Research Project, 2021 – 2024

The study of the processes governing the end of the life of stars such as our Sun (AGB stars) is of fundamental importance. During this phase, the stars undergo extreme mass-loss in which they expel large amounts of material into interstellar space. This material is the main sources of interstellar enrichment. Many questions remain related to the exact processes involved in driving AGB mass-loss. Specifically, the transport of material from the star to the region where dust can form and radiation pressure on dust can accelerate a wind is still poorly understood. Hydrodynamical models provide direct predictions of e.g. density, temperature and velocity fields. But only recently have observations been able to resolve the complex processes going on in the extended stellar atmospheres.In this project, we will use ALMA observations to constrain the physical conditions in AGB extended atmospheres. We have shown that ALMA observations are the only direct probes of density, temperature and dynamics in this region. But we find significant differences between the characteristics predicted by simulations, continuum, and molecular line observations. The project goal is to explain these differences and provide descriptions of AGB atmospheres that will serve as a benchmark for simulations. With improved understanding of the region from which AGB mass-loss originates, proper models for AGB stars can be developed. The stellar yields of these will serve as input for galaxy evolution models.