Letters of Intent received in 2016

LoI 2018-1950
Why Galaxies Care About AGB Stars: A Continuing Challenge through Cosmic Time

Topics

- Stellar structure and evolution to, on, and past the AGB
- Nucleosynthesis, mixing and rotation
- Pulsation, dynamical atmospheres and dust formation
- Physics of circumstellar envelopes of AGB stars and their progeny, planetary nebulae
- Basic ingredients for modelling AGB stars
- Binarity, planets and disks
- AGB stars in the cosmic matter cycle
- Resolved and unresolved AGB populations
- Galaxy evolution, including the first AGB stars
- New and future observational perspectives

Rationale

Stars are conspicuous components of galaxies, and the sites of the creation of most chemical elements in our universe. 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; the final stellar evolutionary stage for the majority of stars that have died in our universe) play an important role, in their capacity as both actors and probes, in our understanding of stellar and galactic evolution. In addition, AGB stars are prime examples of complicated phenomena, where physical and chemical processes, active on different temporal and spatial scales, are at work simultaneously. Therefore, a study of these stars gives deep insights into different processes of great relevance to the understanding of stellar evolution in general.

This symposium aims to build a bridge between research on the 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 on both sides will be discussed to reach an understanding of possibilities, limitations, and needs in both areas, and hence to improve our knowledge about the role of AGB stars in 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, etc. These uncertainties in our understanding of AGB stars directly propagate into the field of extragalactic astronomy, where they affect critically the interpretation of galaxy properties, e.g. stellar masses, ages, and the chemical evolution. The complexity of the objects also makes it difficult for individuals to master all aspects of their role as galaxy inhabitants, a problem that the proposed symposium aims to illuminate and overcome.

New and upcoming major observational facilities like ALMA, Gaia, JWST, LSST, SKA, and the ELTs will provide exciting opportunities to tackle these challenges from the observational side, stretching from the detailed study of individual objects that are spatially resolved to AGB populations in distant galaxies. This makes it particularly important to outline a strategic programme of combined theoretical and observational activities at this time.

We therefore argue strongly that the time is ripe to dedicate an IAU Symposium, to be held in the course of the 30th General Assembly of the IAU in Vienna, to this important interplay between stellar, galactic, and extragalactic research. It will build on the successful tradition of Vienna AGB meetings in 2006, 2010, and 2014, which have all touched upon the theme proposed here “Why Galaxies Care about AGB Stars”, but this time the intent is to significantly widen both scope and audience.