STARLAB: Evolved stars and their shells: Laboratories for stellar physics



BELSPO Institut d'Astronomie et d'Astrophysique, ULB Royal Observatory of BelgiumInstitute of Astronomy, KULeuven

The goal of this project is to boost our understanding of (some of) the physical and chemical processes at work in low- and intermediate-mass (LIMS) stars. Specifically, we plan

  1. to derive the surface abundances in specific LIMS and confront them with nucleosynthesis predictions. Progress is expected from the fact that we will use wellselected targets with known distances (like AGB and post-AGB stars in the Magellanic Clouds or the Galactic Bulge), allowing us to locate them in the Hertzsprung-Russell diagram, thus facilitating the confrontation with the models, or by deriving isotopic ratios (from ALMA data) rather than elemental abundances. The determination of the atmospheric composition of evolved LIMS provides strong diagnostics on the internal nuclear burning and mixing processes at play in the stellar interior. Owing to their rich nucleosynthesis, AGB and post-AGB stars are thus exceptional laboratories to test the robustness of stellar models.
  2. to explore new binary evolutionary channels that may link classes of LIMS in binary systems. Progress is expected from the modeling of physical processes not dealt with so far (tidal interaction with a circumbinary disc for instance, to pump up the orbital eccentricity), and from the recent availability of a key diagnostic tool like the eccentricity– period diagram. The latter is obtained from our on-going effort to monitor the radial velocity of very diverse classes of LIMB to get their orbital elements. After 5 years of operation of our HERMES spectrograph, even wide orbits are now becoming available. Ultimately, this project should assess how the various classes of LIMB as well as their surface composition fit within a global picture.
  3. to study the circumstellar shells around LIMS at different spatial scales using mid-IR interferometry, Herschel and ALMA data. We will address questions on the enigma of the dust formation and condensation process in oxygen-rich stars, and the behaviour of mass-loss as a function of metallicity.