Carbon-enhanced Metal-poor Stars and Thermohaline Mixing

Glebbeek, Evert; Izzard, Robert G.; Pols, O. R.; Stancliffe, Richard J.; Houdek, Guenter; Martin, Rebecca G.; Tout, Christopher A.

doi:10.1063/1.2819015

Cited by 8 publications

(7 citation statements)

References 8 publications

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“…For example, it has been pointed out that vigorous fingering convection might occur in stars (Vauclair 2004;Charbonnel & Zahn 2007;Stancliffe et al 2007), where the resulting transport may account for observed peculiarities in luminosity or metallicity. Our work suggests that, despite the complexity of these highly nonlinear processes, much can still be learned first by obtaining local flux laws for turbulent mixing in the parameter regimes typical of these systems, and then applying the mean-field theory framework as show in Paper I and in this work.…”

Section: Discussion and Prospectsmentioning

confidence: 99%

“…This commonly occurs in a large variety of natural environments, the best studied one being the heat-salt system in the oceanic thermocline (Schmitt 1994;Schmitt et al 2005). Other areas of application range from the Earth's atmosphere (Merceret 1977;Bois & Kubicki 2002) to magmatic melts (Tait & Jaupart 1989) and the interiors of giant planets (Guillot 1999) and stars (Vauclair 2004;Charbonnel & Zahn 2007;Stancliffe et al 2007).…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of fingering convection. Part 2 The formation of thermohaline staircases

et al. 2011

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Regions of the ocean's thermocline unstable to salt fingering are often observed to host thermohaline staircases, stacks of deep well-mixed convective layers separated by thin stably-stratified interfaces. Decades after their discovery, however, their origin remains controversial. In this paper we use 3D direct numerical simulations to shed light on the problem. We study the evolution of an analogous double-diffusive system, starting from an initial statistically homogeneous fingering state and find that it spontaneously transforms into a layered state. By analysing our results in the light of the mean-field theory developed in Paper I, a clear picture of the sequence of events resulting in the staircase formation emerges. A collective instability of homogeneous fingering convection first excites a field of gravity waves, with a well-defined vertical wavelength. However, the waves saturate early through regular but localized breaking events, and are not directly responsible for the formation of the staircase. Meanwhile, slower-growing, horizontally invariant but vertically quasi-periodic γ-modes are also excited and grow according to the γ−instability mechanism. Our results suggest that the nonlinear interaction between these various mean-field modes of instability leads to the selection of one particular γ−mode as the staircase progenitor. Upon reaching a critical amplitude, this progenitor overturns into a fully-formed staircase. We conclude by extending the results of our simulations to real oceanic parameter values, and find that the progenitor γ−mode is expected to grow on a timescale of a few hours, and leads to the formation of a thermohaline staircase in about one day with an initial spacing of the order of one to two metres.

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Section: Discussion and Prospectsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dynamics of fingering convection. Part 2 The formation of thermohaline staircases

et al. 2011

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“…In addition to oceanographic applications, compositionally driven doublediffusive convection affects heat and material transport in a variety of other geo-and astrophysical fluid systems, from magmatic melts (Tait and Jaupart 1989) to the interiors of giant planets and stars (Guillot 1999;Vauclair 2004;Charbonnel and Zahn 2007;Stancliffe et al,, 2007).…”

Section: Equation Section (Next)mentioning

confidence: 99%

Equilibrium transport in double-diffusive convection

2011

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A theoretical model for the equilibrium double-diffusive transport is presented which emphasizes the role of secondary instabilities of salt fingers in saturation of their linear growth. Theory assumes that the fully developed equilibrium state is characterized by the comparable growth rates of primary and secondary instabilities. This assumption makes it possible to formulate an efficient algorithm for computing diffusivities of heat and salt as a function of the background property gradients and molecular parameters. The model predicts that the double-diffusive transport of heat and salt rapidly intensifies with decreasing density ratio. Fluxes are less sensitive to molecular characteristics, mildly increasing with Prandtl number $(\mathit{Pr})$ and decreasing with diffusivity ratio $(\tau )$. Theory is successfully tested by a series of direct numerical simulations which span a wide range of $\mathit{Pr}$ and $\tau $.

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“…Thus, the faster diffuser (temperature T ) is stabilizing and the slower diffuser (salinity S) is destabilizing, resulting in the salt finger form of double-diffusive convection, which is the main focus of our discussion. In addition to oceanographic applications, the compositionally driven double-diffusive convection affects the heat and material transport in a variety of other geo-and astrophysical fluid systems, from magmatic melts (Tait & Jaupart 1989) to the interiors of giant planets and stars (Guillot 1999;Vauclair 2004;Charbonnel & Zahn, 2007;Stancliffe et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Equilibration of weakly nonlinear salt fingers

Radko

2010

J. Fluid Mech.

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An analytical model is developed to explain the equilibration mechanism of the salt finger instability in unbounded temperature and salinity gradients. The theory is based on the weakly nonlinear asymptotic expansion about the point of marginal instability. The proposed solutions attribute equilibration of salt fingers to a combination of two processes: (i) the triad interaction and (ii) spontaneous development of the mean vertical shear. The non-resonant triad interactions control the equilibration of linear growth for moderate and large values of Prandtl number (Pr) and for slightly unstable parameters. For small Pr and/or rigorous instabilities, the mean shear effects become essential. It is shown that, individually, neither the mean field nor the triad interaction models can accurately describe the equilibrium patterns of salt fingers in all regions of the parameter space. Therefore, we propose a new hybrid model, which represents both stabilizing effects in a single framework. The resulting solutions agree with the fully nonlinear numerical simulations over a wide range of governing parameters.

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Carbon-enhanced Metal-poor Stars and Thermohaline Mixing

Cited by 8 publications

References 8 publications

Dynamics of fingering convection. Part 2 The formation of thermohaline staircases

Dynamics of fingering convection. Part 2 The formation of thermohaline staircases

Equilibrium transport in double-diffusive convection

Equilibration of weakly nonlinear salt fingers

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