S343: Why Galaxies Care About AGB Stars

Mass loss during the AGB phase is critical for both the evolution of the star itself and the chemical evolution of the hosting galaxy. In recent years, observations have revealed that its temporal evolution, dynamics, geometry and chemistry are more complex than originally thought. This image shows the detached shell surrounding the carbon star U Antliae as observed by ALMA. (ALMA (ESO / NAOJ / NRAO) / F. Kerschbaum)

Stars are the main components of galaxies and the sites of the creation of most chemical elements. As such, they are the most important ingredients in our physical description of the Universe. Due to their high luminosity and production of heavy elements and cosmic dust, stars on the asymptotic giant branch (AGB) play an important role in their capacity as both actors and probes. In addition, AGB stars are prime laboratories for studying complicated physics, such as hydro-dynamical instabilities, double-shell nuclear burning and dynamical atmospheres where physical and chemical processes, active on different temporal and spatial scales, are at work simultaneously. Understanding these stars sheds light on different processes of great relevance to the understanding of stellar and galactic evolution in general.

IAU Symposium 343, Why Galaxies Care About AGB Stars: A Continuing Challenge Through Cosmic Time, builds a bridge between research on AGB stars themselves and its application to the modelling of stellar populations and the chemical evolution of galaxies and the Universe as a whole. Current developments and challenges viewed from both domains will be discussed to reach an understanding of possibilities, limitations and needs in both areas in an attempt to improve our understanding of the role of AGB stars within the context of galaxies over cosmic time.

Despite the fact that major efforts have being carried out on both observational and theoretical grounds in recent years, our knowledge of AGB stars is still deficient due to uncertainties related to mass loss, convection, mixing, dredge-up efficiencies and the role of binary interaction processes. These uncertainties propagate into the field of extragalactic astronomy where they critically affect the interpretation of galaxy properties such as stellar masses, ages and chemical evolution. The complexity of the objects also makes it difficult for individual researchers to master all aspects of their role as galaxy inhabitants, a problem that Symposium 343 aims to highlight and overcome.

New and upcoming major observational facilities such as the Atacama Large Millimeter/submillimeter Array (ALMA), Gaia, the James Webb Space Telescope (JWST), the Large Synoptic Survey Telescope (LSST), the Square Kilometre Array (SKA), and the 25, 30, and 39 meter extremely large telescopes (ELTs) will provide exciting opportunities for tackling these challenges from the observational side, stretching from the detailed study of individual objects that are spatially resolved to AGB populations in distant galaxies. At the same time, thanks to high-performance computing, 3D modelling of stellar interiors is starting to become feasible, propelling us toward a better understanding of the uncertainties related to the physics of AGB stars. This makes it particularly important to outline a strategic programme of combined theoretical and observational activities at this time.

In order to cover the large breadth of the Symposium, it has been divided into multiple themes, each covered by invited talks, oral contributions and posters:

  • Stellar structure and evolution to, on and past the AGB;
  • Nucleosynthesis, mixing and rotation;
  • Pulsation, dynamic atmospheres and dust formation;
  • Circumstellar envelopes of AGB stars and their progeny, planetary nebulae;
  • Binarity, planets and disks;
  • AGB stars in the cosmic matter cycle;
  • Resolved and unresolved AGB populations in stellar systems; and
  • Galaxy evolution, including the first AGB stars.

Two plenary talks will focus on AGB stars and will provide a broader perspective of interest for research on stars and galaxies in general:

  • Nucleosynthesis (by Amanda Karakas, Monash University, Melbourne, Australia); and
  • New and future observational perspectives (by Eline Tolstoy, Kapteyn Institute, Groningen, Netherlands).

HANS OLOFSSON is professor of radio astronomy at the Department of Space, Earth and Environment at Chalmers University of Technology, Gothenburg, Sweden. His main research area is the circumstellar medium around evolved stars.

FRANZ KERSCHBAUM is professor of observational astrophysics at the Department of Astrophysics at the University of Vienna, Austria. His main research areas include late stages of stellar evolution, instrumentation for astronomical space missions and the history of astronomy.

PAOLA MARIGO is professor of stellar evolution and nucleosynthesis at the Department of Physics and Astronomy, University of Padova, Italy. She is the principal investigator of the STARKEY project on AGB stars, funded by the ERC Consolidator Grant scheme.