Sommaire:

Transport processes occurring in the radiative interior of solar-type stars and low-mass stars are evidenced by the surface variation of light elements, in particular lithium (Li) and beryllium (Be), as well as by the evolution of the stellar rotation rate. While there are many independent transport models for angular momentum and chemical species, there is a lack of self-consistent theories that permit stellar evolution models to simultaneously match the present-day observations. Low-mass stars (F- to K- spectral type) of Population I are characterised by an important Li-depletion during their evolution from the pre-main sequence to the age of the Sun, as well as the so-called Li-dip (and Be-dip) for F-type stars and observed for a few open clusters like the Hyades. Rotation-induced mixing has been seen as an insufficient process to fully explained the observed Li depletion. The aim of the PhD thesis is to explore how additional transport processes can improve the agreement between evolutionary models and observational constraints. Using the stellar evolution code STAREVOL, we explored several transport processes from the literature for chemicals and for angular momentum (penetrative convection, tachocline mixing, additional turbulence, additional viscosity). The need for additional transport processes in stellar evolution models for both chemicals and angular momentum in addition to atomic diffusion, meridional circulation, and turbulent shear is confirmed. We identified the rotational dependence of the penetrative convection as a key process. Two additional and distinct parametric turbulent mixing processes (one for angular momentum and one for chemicals) are required to simultaneously explain the observed surface Li depletion and the solar internal rotation profile. This is also necessary for a larger range of masses from 0.8 to 1.2 Msol in order to reproduce the Li depletion trend with decreasing effective temperature on the cold side of the dip. Finally, the Li (and Be) dip, for stars of mass 1.3-1.5 Msol, displays a different trend, and we have shown that a readjustment of the prescription and parameters, notably for shear turbulence and magnetic braking, are needed to reproduce it.

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