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The observations of global stellar oscillations of post main-sequence starsby space-based photometry missions allowed to directly determine their internalrotation. These constraints have pointed towards the existence of angularmomentum transport processes unaccounted for in theoretical models.Constraining the properties of their internal rotation thus appears as thegolden path to determine the physical nature of these missing dynamicalprocesses. We wish to determine the robustness of a new approach to study theinternal rotation of post main-sequence stars, using parametric rotationprofiles coupled to a global optimization technique. We test our methodology onKepler 56, a red giant observed by the Kepler mission. First, we carry out anextensive modelling of the star using global and local minimizationstechniques, and seismic inversions. Then, using our best model, we study indetails its internal rotation profile, we adopted a Bayesian approach toconstrain stellar parametric predetermined rotation profiles using a MonteCarlo Markov Chain analysis of the rotational splittings of mixed modes. OurMonte Carlo Markov Chain analysis of the rotational splittings allows todetermine the core and envelope rotation of Kepler 56 as well as give hintsabout the location of the transition between the slowly rotating envelope andthe fast rotating core. We are able to discard a rigid rotation profile in theradiative regions followed by a power-law in the convective zone and show thatthe data favours a transition located in the radiative region, as predicted byprocesses originating from a turbulent nature. Our analysis of Kepler 56indicates that turbulent processes whose transport efficiency is reduced bychemical gradients are favoured, while large scale fossil magnetic fields aredisfavoured as a solution to the missing angular momentum transport.

astronomy and astrophysics

Asteroseismology of evolved stars to constrain the internal transport of  angular momentum. IV. Internal rotation of Kepler 56 from an MCMC analysis of  the rotational splittings