Double-Diffusive Mixing in Stellar Interiors in the Presence of Horizontal Gradients

Medrano, Michael; Garaud, Pascale; Stellmach, Stephan

doi:10.1088/2041-8205/792/2/l30

Cited by 12 publications

(16 citation statements)

References 21 publications

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“…Several other 3D simulations of thermohaline mixing have been conducted in recent years (Denissenkov & Merryfield 2011;Traxler et al 2011;Brown et al 2013;Medrano et al 2014;Garaud & Brummell 2015). Denissenkov & Merryfield (2011) compared their 3D work to the 2D simulations of Denissenkov (2010) and confirmed the results from the 2D simulations, as well as finding the excitation of gravity waves in their oceanic case but not their RGB case.…”

Section: Discussionmentioning

confidence: 56%

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A phenomenological modification of thermohaline mixing in globular cluster red giants

Henkel¹,

Karakas²,

Lattanzio³

2017

Monthly Notices of the Royal Astronomical Society

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Thermohaline mixing is a favoured mechanism for the so-called "extra mixing" on the red giant branch of low-mass stars. The mixing is triggered by the molecular weight inversion created above the hydrogen shell during first dredge-up when helium-3 burns via 3 He( 3 He,2p) 4 He. The standard 1D diffusive mixing scheme cannot simultaneously match carbon and lithium abundances to NGC 6397 red giants. We investigate two modifications to the standard scheme: (1) an advective two stream mixing algorithm, and (2) modifications to the standard 1D thermohaline mixing formalism. We cannot simultaneously match carbon and lithium abundances using our two stream mixing approach. However we develop a modified diffusive scheme with an explicit temperature dependence that can simultaneously fit carbon and lithium abundances to NGC 6397 stars. Our modified diffusive scheme induces mixing that is faster than the standard theory predicts in the hotter part of the thermohaline region and mixing that is slower in the cooler part. Our results infer that the extra mixing mechanism needs further investigation and more observations are required, particularly for stars in different clusters spanning a range in metallicity.

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Section: Discussionmentioning

confidence: 56%

“…as the Prandtl number decreases), with the thermohaline fingers becoming more like blobs (Traxler et al 2011). Subsequent studies found that thermohaline fingers became blobs over time (Brown et al 2013;Medrano et al 2014;Garaud & Brummell 2015).…”

Section: Discussionmentioning

confidence: 98%

A phenomenological modification of thermohaline mixing in globular cluster red giants

Henkel¹,

Karakas²,

Lattanzio³

2017

Monthly Notices of the Royal Astronomical Society

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“…This quantity might be considered important because zonal jets grow to sizes comparable with the box, so that the dynamics of the jets could be affected by the periodic boundary conditions. For example, the dynamics of double-diffusive intrusions, in which similar (though not directly analogous) large-scale inclined structures are generated (Simeonov & Stern 2007;Medrano et al 2014), is affected by the degree of inclina-tion of the box relative to the intrusions. In Fig.…”

Section: Evolution In Larger Boxes and Different Aspectmentioning

confidence: 99%

Angular momentum transport, layering, and zonal jet formation by the GSF instability: non-linear simulations at a general latitude

Barker

Jones

Tobias

2020

Monthly Notices of the Royal Astronomical Society

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We continue our investigation into the non-linear evolution of the Goldreich–Schubert–Fricke (GSF) instability in differentially rotating radiation zones. This instability may be a key player in transporting angular momentum in stars and giant planets, but its non-linear evolution remains mostly unexplored. In a previous paper we considered the equatorial instability, whereas here we simulate the instability at a general latitude for the first time. We adopt a local Cartesian Boussinesq model in a modified shearing box for most of our simulations, but we also perform some simulations with stress-free, impenetrable, radial boundaries. We first revisit the linear instability and derive some new results, before studying its non-linear evolution. The instability is found to behave very differently compared with its behaviour at the equator. In particular, here we observe the development of strong zonal jets (‘layering’ in the angular momentum), which can considerably enhance angular momentum transport, particularly in axisymmetric simulations. The jets are, in general, tilted with respect to the local gravity by an angle that corresponds initially with that of the linear modes, but which evolves with time and depends on the strength of the flow. The instability transports angular momentum much more efficiently (by several orders of magnitude) than it does at the equator, and we estimate that the GSF instability could contribute to the missing angular momentum transport required in both red giant and subgiant stars. It could also play a role in the long-term evolution of the solar tachocline and the atmospheric dynamics of hot Jupiters.

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“…Out of the models without braking, on the main sequence the j a = 1 × 10 16 cm 2 s −1 model is the one most similar in terms of surface rotation velocity, and the j a = 7 × 10 16 cm 2 s −1 model is the one most similar in terms of surface abundances. However, many authors (Denissenkov & Pinsonneault 2008a;Vauclair & Théado 2012;Maeder et al 2013) have argued that the strong horizontal turbulence expected in rotating stars (Zahn 1992) should at least curtail thermohaline mixing, if not outright suppress it (also see Medrano et al 2014). If so, it might be more appropriate to exclude thermohaline mixing.…”

Section: Comparison To Observationsmentioning

confidence: 99%

Rotational mixing in carbon-enhanced metal-poor stars withs-process enrichment

Matrozis

Stancliffe

2017

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Carbon-enhanced metal-poor (CEMP) stars with s-process enrichment (CEMP-s) are believed to be the products of mass transfer from an asymptotic giant branch (AGB) companion, which has long since become a white dwarf. The surface abundances of CEMP-s stars are thus commonly assumed to reflect the nucleosynthesis output of the first AGB stars. We have previously shown that, for this to be the case, some physical mechanism must counter atomic diffusion (gravitational settling and radiative levitation) in these nearly fully radiative stars, which otherwise leads to surface abundance anomalies clearly inconsistent with observations. Here we take into account angular momentum accretion by these stars. We compute in detail the evolution of typical CEMP-s stars from the zero-age main sequence, through the mass accretion, and up the red giant branch for a wide range of specific angular momentum j a of the accreted material, corresponding to surface rotation velocities, v rot , between about 0.3 and 300 km s −1 . We find that only for j a 10 17 cm 2 s −1 (v rot > 20 km s −1 , depending on mass accreted) angular momentum accretion directly causes chemical dilution of the accreted material. This could nevertheless be relevant to CEMP-s stars, which are observed to rotate more slowly, if they undergo continuous angular momentum loss akin to solar-like stars. In models with rotation velocities characteristic of CEMP-s stars, rotational mixing primarily serves to inhibit atomic diffusion, such that the maximal surface abundance variations (with respect to the composition of the accreted material) prior to first dredge-up remain within about 0.4 dex without thermohaline mixing or about 0.5-1.5 dex with thermohaline mixing. Even in models with the lowest rotation velocities (v rot 1 km s −1 ), rotational mixing is able to severely inhibit atomic diffusion, compared to non-rotating models. We thus conclude that it offers a natural solution to the problem posed by atomic diffusion and cannot be neglected in models of CEMP-s stars.

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Double-Diffusive Mixing in Stellar Interiors in the Presence of Horizontal Gradients

Cited by 12 publications

References 21 publications

A phenomenological modification of thermohaline mixing in globular cluster red giants

A phenomenological modification of thermohaline mixing in globular cluster red giants

Angular momentum transport, layering, and zonal jet formation by the GSF instability: non-linear simulations at a general latitude

Rotational mixing in carbon-enhanced metal-poor stars withs-process enrichment

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