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Chemical element transport in stars. Uncertainties and their impact on the study of stellar populations

Maurizio Salaris

Stellar evolution computations provide the foundation of several methods
applied to study the evolutionary properties of stars and stellar
populations.
One particularly thorny issue is how to treat the transport of chemical
elements in stellar evolution calculations. Mixing and element transport
do not arise from the solution of the equations of stellar structure and
evolution, instead they have to be added following recipes that involve
a number of free parameters and/or are subject to sizable uncertainties.
At the same time, the temporal evolution of the chemical profiles within
stellar models is a main evolutionary driver, and can be in principle
tested through spectroscopic observations of photospheric abundances of
key elements, asteroseismic observations, and more indirectly through
the effect on star counts (sensitive to evolutionary timescales) and
evolutionary paths in colour-magnitude-diagrams, that are all affected
by the internal chemical profiles.