Global 3D models of AGB stars and Red Supergiants with winds

The Swedish Research Council reached a decision on October 31, 2019 on project grants and starting grants for Natural and Engineering Sciences. The Department of Physics and Astronomy is granted 40 840 000 SEK for the period 2020-2023 for in total nine project grants and three starting grants. The projects will begin during 2020.

Project description

Project title: Global 3D models of AGB stars and Red Supergiants with winds
Main applicant: Susanne Höfner, Division of Astronomy and Space Physics
Grant amount: 3 825 000 SEK for the period 2020-2023
Funder: Project grant from the Swedish Research Council

Cool giant and supergiant stars are sources of massive outflows, which determine their final fate. Low- to intermediate-mass stars lose a significant fraction of their mass during the Asymptotic Giant Branch (AGB) phase and evolve into white dwarfs. Massive stars, despite substantial mass loss in the Red Supergiant (RSG) phase, exceed the critical mass and explode as supernovae.

The wind mechanism of AGB stars involves two steps: atmospheric shock waves (due to convection and pulsation) and radiation pressure on dust grains, forming in the dense wakes of the shocks. Current 1D wind models produce realistic mass-loss rates, but involve free parameters and cannot account for the complex 3D morphology of the dusty atmospheres found in recent high-angular-resolution observations, presumably caused by large-scale convective flows. Building on our 3D “star-in-a-box” models, we will produce a new type of global 3D radiation-hydrodynamical (RHD) simulations, i.e. self-consistent “star-and-wind-in-a-box” models.

For RSG stars, several wind mechanisms have been suggested (radiation pressure on molecules or dust, Alfvén waves) but at present there are no realistic models to test these ideas. Global 3D RHD simulations reproduce observed convective surface patterns, but not the large radial extension of the atmospheres. This hints at an incompleteness in the physical description, which will be addressed in this project to solve the long-standing problem of wind-driving in RSG stars.

Stellar winds on the research pages of Astronomy and Space Physics