Mass-losing AGB stars and Supergiants

A COOL STARS 19 splinter session

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The Fried Egg nebula.
Image credit: Eric Lagadec

Artist's impression of a giant flare on the surface of red giant Mira A. Behind the star, material is falling onto the star's tiny companion, Mira B.
Image credit: Katja Lindblom, CC BY-NC-ND 4.0

Session organizers


There have been extraordinary advances in our knowledge of asymptotic giant branch (AGB) stars over the last decade. On the observational side results from Spitzer, Herschel, VERA and ALMA in particular have provided access to the wavelength ranges in which these stars and their associated dust and molecular shells emit most of their energy. Interferometry has enabled convection cells to be resolved and has highlighted the role of binary interactions in the mass-loss process from these huge stars. At the same time theoretical advances give us a better understanding of element formation, 3D models of convection, and new insight into the properties of grains produced in the very extended circumstellar environments. Nucleosynthesis models are making testable predictions and population synthesis models are reproducing many of the characteristics of highly evolved stars, for the first time.

This splinter session will be split over 2 afternoons as follows:

Monday 6 June

Session (1): From waves to winds: gas dynamics in evolved stars
Luminous cool giants are strongly affected by dynamical processes. Large-scale convective motions and stellar pulsation trigger sound waves, which may develop into strong shock waves as they propagate outwards through the stellar atmospheres. These shocks, possibly supported by other physical processes (rotation, magnetic fields), intermittently lift gas to distances where dust grains can form and trigger a stellar wind. Recent developments in instrumentation allow us to image the relevant regions in ever increasing detail over a wide wavelength range, from the optical to the radio regime (e.g., VLTI, CHARA, ALMA), giving unprecedented insights into these phenomena. At the same time, dynamical models of interior dynamics (3D convection, pulsation) and of atmospheres and winds have reached a level where they permit self-consistent quantitative simulations of these processes. Significant progress can be expected from a detailed confrontation of latest 3D models and imaging observation.

Tuesday 7 June

Session (2): The circumstellar environment of cool giants and supergiants
Evolved stars eject much of their mass into space through extreme winds. The ejecta form an expanding shell around the star, extending from the dust formation radius at 2 stellar radii to the asteropause at 1-4 parsec where the merger with the interstellar medium takes place. Although the winds are thought to be largely spherically symmetric, recent observations show growing evidence for strong shaping. The ESO VLT and ALMA have found evidence for spirals, circumstellar disks, bipolar flows and jets, and even wind-blown tails. The dominant shaping mechanisms is believed to be angular momentum, which for most of stellar evolution is in cold storage in stellar, sub-stellar and planetary companions, but is transferred to the shells through dynamical interactions. Related processes act in supergiants and their supernovae, common envelope systems and stellar mergers: together the stars cover most of the HR diagram. We will bring together observers and theoreticians to discuss the shaping mechanisms over a wide range of stellar properties. Topics will include the new observations at extreme angular resolution (e.g. Sphere, ALMA), 3D hydrodynamical models, planetary systems around evolved stars, and common envelope evolution.

Invited Speakers

Session 1: Elizabeth Humphreys and Claudia Paladini
Session 2: Eric Lagadec and Shazrene Mohamed
Invited plenary speakers covering AGB stars: Amanda Karakas and Susanne Höfner


The program and the list of abstracts are published on dedicated webpages that you can reach from the links below.



More information from Susanne Hoefner at susanne.hoefner@physics.uu.se or Patricia Whitelock at paw@saao.ac.za.