A tale of giants and how they start losing mass
Thesis Supervisor: Claudia Paladini
Abstract
Stars with low to intermediate initial mass (≲ 8 M⊙), including our Sun, undergo a short evolutionary phase, called the Asymptotic Giant Branch (AGB). Stars on the AGB usually have O-rich chemistry. However, after the so-called third dredge-up, stars with initial masses between 1 and 4 M⊙ can reach a C/O ratio > 1, and their spectra are then dominated by C-bearing molecular and dust species. The atmosphere of a star on the AGB can be as large as a few au, and it is stripped away by a stellar wind on a typical time-scale of thousands of years. The material stripped away feeds the interstellar medium becoming a building block for the new generation of stars, planets, and eventually life.Therefore the mass-loss process is a key ingredient for our understanding of many fields of astrophysics, including stellar evolution and the chemical enrichment of the interstellar medium via stellar yields.
Within the frame of the study of mass-loss in galactic AGB stars we propose the following thesis topics:
Characterise convection mechanism as function of stellar parameters
Study of dust obscuration events
From molecules to dust: characterising the dust stratification of O-rich AGBs
The role of binaries in the mass-loss process
The thesis are all based on existing data sets from the various VLTI instruments (GRAVITY, PIONIER, MATISSE, but also archive unpublished data from AMBER and MIDI), and from single dish instruments such as for example VISIR and SPHERE. The data will be compared with state-of-the-art model atmospheres. The student will interact with the primary ESO/Chile supervisor, and depending on the project selected also with colleagues from ESO/Chile and ESO/Garching, from ALMA, and theoreticians which are already long term collaborators of the ESO primary advisor.