Hydrodynamic simulations of convection and nucleosynthesis in the late phases of massive stars to constrain and guide stellar evolution theory

Rizzuti, Federico

Abstract

The present knowledge of stellar evolution is still limited today by large uncertainties that derive from the complex multi-dimensional processes occurring in stars. Among them, the turbulent motions of the stellar fluid control the size and evolution of convective zones, deeply affecting the structure and evolution of the star. The weaknesses of the current theories include determining the extent of the convective regions, the amount of mixing at the convective boundaries, and the exact evolution and death of convection.
Convection and its effects are normally included in one-dimensional stellar evolution models by means of simplifying prescriptions, that need to be calibrated from observations or numerical simulations to correctly represent the stellar physics. Hydrodynamic models of stars can improve these prescriptions by studying realistic multi-D processes in great detail, but only for a short time range compared to the entire stellar evolution.
In this thesis, I present the results from three new sets of 3D hydrodynamic simulations, each exploring a different stellar environment, with the aim of studying turbulent motions and nucleosynthesis in convective regions of evolved massive stars. The analysis has been performed by studying both the dynamics of the fluid and the evolution of the chemical abundances. The results show that late convective phases of massive stars present very strong boundary mixing, but the overshooting prescription calibrated from the new 3D data displays a new-found convergence towards 1D models results. The analysis of the abundances and their evolution shows the production and consumption by nuclear reactions, in addition to the transport of species and their dispersion across the layers.
These conclusions help answer some open questions in stellar evolution theory, and they can have an important impact on our understanding of stellar structure and evolution.

Citation

Rizzuti, F. (2023). Hydrodynamic simulations of convection and nucleosynthesis in the late phases of massive stars to constrain and guide stellar evolution theory. (Thesis). Keele University. Retrieved from https://keele-repository.worktribe.com/output/674565

• Thesis Type: Thesis
• Deposit Date: Dec 21, 2023
• Publicly Available Date: Mar 6, 2024
• Public URL: https://keele-repository.worktribe.com/output/674565
• Additional Information: Embargo on access until 1 March 2024 - The thesis is due for publication, or the author is actively seeking to publish this material.
• Award Date: 2023-12