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Thanks to asteroseismology, constraints on the core rotation rate areavailable for hundreds of low- and intermediate-mass stars in evolved phases.Current physical processes tested in stellar evolution models cannot reproducethe evolution of these core rotation rates. We investigate the efficiency ofthe internal angular momentum redistribution in red giants during the hydrogenshell and core-helium burning phases based on the asteroseismic determinationsof their core rotation rates. We compute stellar evolution models with rotationand model the transport of angular momentum by the action of a sole dominantdiffusive process parametrized by an additional viscosity. We constrain thevalues of this viscosity to match the mean core rotation rates of red giantsand their behaviour with mass and evolution along the red giant branch and inthe red clump. For red giants in the hydrogen shell-burning phase the transportof angular momentum must be more efficient in more massive stars. Theadditional viscosity is found to vary by approximately two orders of magnitudein the mass range M $\sim$ 1 - 2.5 M$_{\odot}$. As stars evolve along the redgiant branch, the efficiency of the internal transport of angular momentum mustincrease for low-mass stars (M $\lesssim$ 2 M$_{\odot}$) and remainapproximately constant for slightly higher masses (2.0 M$_{\odot}$ $\lesssim$ M$\lesssim$ 2.5 M$_{\odot}$). In red-clump stars, the additional viscositiesmust be an order of magnitude higher than in younger red giants of similar massduring the hydrogen shell-burning phase. In combination with previous efforts,we obtain a clear picture of how the physical processes acting in stellarinteriors should redistribute angular momentum from the end of the mainsequence until the core-helium burning phase for low- and intermediate-massstars to satisfy the asteroseismic constraints.

astronomy and astrophysics

Asteroseismology of evolved stars to constrain the internal transport of  angular momentum. V. Efficiency of the transport on the red giant branch and  in the red clump