Evolution of the core rotation of stars on the red giant branch: from large-scale measurements towards a caracterisation of the angular momentum transport
Résumé
Asteroseismology consists in probing stellar interiors through the detection of seismic waves. Red giants are evolved low-mass stars that have exhausted hydrogen in their core. These stars are solar-type pulsators presenting mixed modes that allow us to have a direct access to the physical properties of their core. The available seismic measurements indicate that one or several mechanisms that remain poorly understood counterbalance the acceleration of the core rotation, resulting from its contraction, by transporting angular momentum. The greatest part of this PhD thesis was devoted to the development of a method allowing a measurement as automated as possible of the mean core rotation of stars on the red giant branch that were observed by the Kepler satellite (NASA). The measurements that were derived for almost 900 stars highlight that the core rotation is almost constant along the red giant branch, with values largely independent of the stellar mass. The second part of this PhD thesis is devoted to the interpretation of these results based on stellar modelling. The challenge consists in using the large-scale measurements obtained in the first part to characterise the quantity of angular momentum that has to be extracted from each layer of the core, at different timesteps on the red giant branch, for different stellar masses.