Fingering convection in red giants revisited

Wachlin, F. C.; Vauclair, S.; Althaus, Leandro Gabriel

doi:10.1051/0004-6361/201424580

Cited by 24 publications

(22 citation statements)

References 37 publications

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“…Fingering convection was also invoked in the case of a local µ-decrease due to nuclear reactions as in Red Giants (Charbonnel & Zahn 2007), although the effect is too small to account for the observations (e.g. Wachlin et al 2014). We are interested in the case of a local heavy element accumulation due to radiative accelerations that lead to an increase of µ.…”

Section: Treatment Of Fingering Convectionmentioning

confidence: 99%

Hydrodynamical instabilities induced by atomic diffusion in A stars and their consequences

Deal

Richard

Vauclair

2016

A&A

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Aims. Atomic diffusion, including the effect of radiative accelerations on individual elements, leads to important variations of the chemical composition inside the stars. The accumulation in specific layers of the elements, which are the main contributors of the local opacity, leads to hydrodynamical instabilities that modify the internal stellar structure and surface abundances. Our aim is to study these effects and compare the resulting surface abundances with spectroscopic observations Methods. We computed the detailed structure of A-type stars including these effects. We used the Toulouse-Geneva Evolution Code (TGEC), where radiative accelerations are computed using the single valued parameter (SVP) method, and we added doublediffusive convection with mixing coefficients deduced from three-dimensional (3D) simulations. Results. We show that the modification of the initial chemical composition has important effects on the internal stellar mixing and leads to different surface abundances of the elements. The results fit the observed surface chemical composition well if the layers, which are individually mixed by double-diffusive convection, are connected.

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Section: Treatment Of Fingering Convectionmentioning

confidence: 99%

Hydrodynamical instabilities induced by atomic diffusion in A stars and their consequences

Deal

Richard

Vauclair

2016

A&A

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“…These simulations currently show that double diffusive instability is not efficient enough to significantly change surface abundances (Wachlin et al 2014). However, they are still far from the parameter space relevant to the stellar regime.…”

Section: Introductionmentioning

confidence: 95%

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

Lagarde

Miglio

Eggenberger

et al. 2015

A&A

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Context. The availability of asteroseismic constraints for a large sample of red giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations. Aims. We use a detailed spectroscopic study of 19 CoRoT red giant stars to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars. Methods. In order to explore the effects of rotation-induced mixing and thermohaline instability, we compare surface abundances of carbon isotopic ratio and lithium with stellar evolution predictions. These chemicals are sensitive to extra-mixing on the red giant branch. Results. We estimate mass, radius, and distance for each star using the seismic constraints. We note that the Hipparcos and seismic distances are different. However, the uncertainties are such that this may not be significant. Although the seismic distances for the cluster members are self consistent they are somewhat larger than the Hipparcos distance. This is an issue that should be considered elsewhere. Models including thermohaline instability and rotation-induced mixing, together with the seismically determined masses can explain the chemical properties of red giant targets. However, with this sample of stars we cannot perform stringent tests of the current stellar models. Tighter constraints on the physics of the models would require the measurement of the core and surface rotation rates, and of the period spacing of gravity-dominated mixed modes. A larger number of stars with longer times series, as provided by Kepler or expected with Plato, would help ensemble asteroseismology.

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“…The predictive power of stellar evolution codes is limited by large uncertainties related to our poor knowledge of these (magneto-)hydrodynamical processes and by the fact that, being fundamentally 3D, they cannot be included self-consistently in 1D computations. Some evolution codes include rotation (Meynet et al 2013) or other 3D processes, such as overshoot (Moravveji et al 2015), semi-convection (Ding & Li 2014), thermohaline mixing (Wachlin et al 2014), or the magnetorotational instability (Wheeler et al 2015). However, these processes, including convection itself, are described by phenomenological models which involve free parameters.…”

Section: Introductionmentioning

confidence: 99%

Shear mixing in stellar radiative zones

Prat

Guilet

Viallet

et al. 2016

A&A

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Context. Recent numerical simulations suggest that the model by Zahn (1992, A&A, 265, 115) for the turbulent mixing of chemical elements due to differential rotation in stellar radiative zones is valid. Aims. We investigate the robustness of this result with respect to the numerical configuration and Reynolds number of the flow. Methods. We compare results from simulations performed with two different numerical codes, including one that uses the shearingbox formalism. We also extensively study the dependence of the turbulent diffusion coefficient on the turbulent Reynolds number. Results. The two numerical codes used in this study give consistent results. The turbulent diffusion coefficient is independent of the size of the numerical domain if at least three large turbulent structures fit in the box. Generally, the turbulent diffusion coefficient depends on the turbulent Reynolds number. However, our simulations suggest that an asymptotic regime is obtained when the turbulent Reynolds number is larger than 10 3 . Conclusions. Shear mixing in the regime of small Péclet numbers can be investigated numerically both with shearing-box simulations and simulations using explicit forcing. Our results suggest that Zahn's model is valid at large turbulent Reynolds numbers.

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Fingering convection in red giants revisited

Cited by 24 publications

References 37 publications

Hydrodynamical instabilities induced by atomic diffusion in A stars and their consequences

Hydrodynamical instabilities induced by atomic diffusion in A stars and their consequences

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

Shear mixing in stellar radiative zones

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