Abstract
Stellar evolution computations provide the foundation of several methods applied to study the evolutionary properties of stars and stellar populations, both Galactic and extragalactic. The accuracy of the results obtained with these techniques is linked to the accuracy of the stellar models, and in this context the correct treatment of the transport of chemical elements is crucial. Unfortunately, in many respects calculations of the evolution of the chemical abundance profiles in stars are still affected by sometimes sizable uncertainties. Here, we review the various mechanisms of element transport included in the current generation of stellar evolution calculations, how they are implemented, the free parameters and uncertainties involved, the impact on the models and the observational constraints.
Highlights
Almost a century ago Eddington wrote [1]: ‘It is reasonable to hope that in a not too distant future we shall be competent to understand so simple a thing as a star’
Surface convection is very important when comparing the surface abundances measured from spectroscopy with the models, because of the dredge-up phenomenon, whereby the fully mixed convective envelopes reach layers processed by nuclear burnings, altering their chemical composition during the red giant branch (RGB) and asymptotic giant branch (AGB) phases [2]
A tricky issue for modelling rotating stars with 1D stellar models is how to describe the transport of angular momentum—that determines the evolution of Ω—and the chemical mixing associated with rotation
Summary
Almost a century ago Eddington wrote [1]: ‘It is reasonable to hope that in a not too distant future we shall be competent to understand so simple a thing as a star’. The aim of this review is to discuss the various mechanisms of chemical element transport included in the current generation of stellar models, their effect on the evolutionary properties of the models, and the various prescriptions found in the literature, that often produce very different results. This will allow the reader to appreciate the main uncertainties involved, and what properties of stellar models are affected the most.
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