Stellar structure, evolution and nucleosynthesis

Abstract

After a brief introduction, we focus on a few key physical ingredients for the evolution of stars and the related nucleosynthesis, namely mass loss, convection and rotation. We first review the current status of their uncertainties and then discuss their impact. Concerning convection, we list key existing and future 3D hydrodynamics simulations needed to constrain prescriptions used in the modelling of convective boundaries in 1D codes. We then discuss the impact of rotation on the s process in both massive and low-mass stars. Massive star models including rotation-induced mixing reproduce much better several observational constraints (e.g. primary nitrogen production and boosted weak s process). AGB models including rotation, on the other hand, fail to produce s process although codes using different prescriptions yield contradictory results. The inclusion of the interaction of rotation with magnetic fields has a positive effect on the predicted spin of white dwarfs. We investigated the impact of this interaction on the 13 C-pocket and find that magnetic fields may also help rotating stars produce more (rather than less) s-process. Current uncertainties in the treatment of convection, rotation and magnetic fields limit the predictive power of stellar evolution models and different implementations in codes lead to different results. Combining 3D hydrodynamics simulations and theoretical work with observational constraints will be needed to improve the situation. In this context, nucleosynthetic signatures of these processes will play a key role as they have up to now.

One size does not fit all: Evidence for a range of mixing efficiencies in stellar evolution calculations

“…A complete chemical mixing profile should include the effects of entrainment, penetration, overshooting, semi-convection, and mixing induced by rotational instabilities and internal gravity waves (Langer 2012;Maeder 2009;Hirschi et al 2014;Arnett et al 2015;Rogers & McElwaine 2017;Salaris & Cassisi 2017). Unfortunately, discussion of chemical mixing mechanisms in the literature suffers from a problem of mixed identities.…”

Modelling of the B-type binaries CW Cephei and U Ophiuchi

“…In general, both element and angular momentum transport processes throughout a star are poorly calibrated (Aerts et al 2019). It is a well-known shortcoming of most 1D theoretical descriptions of convection that convective boundaries are not well described (Hirschi et al 2014). Proposed as a means to remedy this shortcoming, convective core overshooting was included as a way to increase near-core mixing in evolutionary models; it is now highly debated, with several competing studies claiming that models with and without overshooting can reproduce observed binaries across different mass ranges and evolutionary stages (Andersen et al 1990;Schroder et al 1997;Pols et al 1997;Claret 2007 Constantino & Baraffe 2018).…”