Transport processes in red giant stars

Abstract

Low-mass stars (<2–2.5 M_๏) exhibit, at all the stages of theirevolution, signatures of processes that require challenging modelingbeyond the standard stellar theory.In this paper we focus on their peculiarities while they climb thered giant branch (RGB).We first review canonical evolution along the RGB and compare theclassicle predictions of the so-called first dredge-upwith observational data in various environments.We show how clear spectroscopic diagnostics probe the nucleosynthesisand the internal mixing mechanisms that drive RGB stars.Coherent data reveal in particular the existence of a nonstandardand shallow mixing process that changes the surface abundances at the so-called RGB bump.We discuss the current understanding of the connection betweenthis extra-mixing and stellar rotation and conclude on the remaining open questions.