Abstract
Thermohaline mixing has been recently identified as the probable dominating process that governs the photospheric composition of low-mass bright red giant stars. Here, we present the predictions of stellar models computed with the code STAREVOL including this process together with rotational mixing. We compare our theoretical predictions with recent observations, and discuss the effects of both mechanisms on asteroseismic diagnostics.
Highlights
At all stages of their evolution, low- and intermediate-mass stars (LIMS) exhibit the signatures of complex physical processes that require challenging modelling beyond canonical stellar theory.Rotation has been shown to change the internal dynamics of these stars, by means of the transport of both angular momentum and chemical species through the action of meridional circulation and shear turbulence
Thermohaline mixing has been recently identified as the probable dominating process that governs the photospheric composition of low-mass bright red giant stars
[3] identified thermohaline mixing as the process that may govern the surface abundances of LIMS evolving on the upper end of the red giant branch (RGB)
Summary
At all stages of their evolution, low- and intermediate-mass stars (LIMS) exhibit the signatures of complex physical processes that require challenging modelling beyond canonical (or standard) stellar theory (by canonical we refer to the modelling of non-rotating, non-magnetic stars, in which convection is the only mechanism that drives mixing in stellar interiors). [3] identified thermohaline mixing as the process that may govern the surface abundances of LIMS evolving on the upper end of the red giant branch (RGB) In these stars, this doublediffusive instability is induced by the mean molecular weight inversion created by the 3He(3He, 2p)4He reaction in the radiative layers between the convective envelope and the hydrogen burning shell [4]. EFFECTS OF THERMOHALINE INSTABILITY AND ROTATION-INDUCED MIXING ON SURFACE ABUNDANCES 2.1 Carbon isotopic ratio The behaviour of the carbon isotopic ratio is the best indicator of non-standard transport processes in evolved low-mass stars This quantity has been determined in a large number of stars in Galactic open clusters. No thermohaline mixing occurs on the too short RGB phase, and rotation-induced mixing alone explains very well the data
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