On the dynamical interaction between overshooting convection and an underlying dipole magnetic field – I. The non-dynamo regime

Korre, Lydia; Brummell, NH; Garaud, Pascale; Guervilly, Céline

doi:10.1093/mnras/stab477

Cited by 8 publications

(4 citation statements)

References 42 publications

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“…More work is required to obtain reliable determinations of an overshooting depth and to describe quantitatively the mixing and impact on the temperature gradient. Understanding the effects of rotation and magnetic fields on overshooting is a significantly more difficult theoretical and numerical problem to address; however, efforts to study these combined non-linear effects are ongoing (Hotta 2017;Korre et al 2021). Despite the limitations of existing hydrodynamical simulations, they are already providing constraints on physical processes usually treated with several free parameters in 1D stellar evolution models.…”

Section: Discussionmentioning

confidence: 99%

Local heating due to convective overshooting and the solar modelling problem

Baraffe

Constantino

Clarke

et al. 2022

A&A

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Recent hydrodynamical simulations of convection in a solar-like model suggest that penetrative convective flows at the boundary of the convective envelope modify the thermal background in the overshooting layer. Based on these results, we implement in one-dimensional stellar evolution codes a simple prescription to modify the temperature gradient below the convective boundary of a solar model. This simple prescription qualitatively reproduces the behaviour found in the hydrodynamical simulations, namely a local heating and smoothing of the temperature gradient below the convective boundary. We show that introducing local heating in the overshooting layer can reduce the sound-speed discrepancy usually reported between solar models and the structure of the Sun inferred from helioseismology. It also affects key quantities in the convective envelope, such as the density, the entropy, and the speed of sound. These effects could help reduce the discrepancies between solar models and observed constraints based on seismic inversions of the Ledoux discriminant. Since mixing due to overshooting and local heating are the result of the same convective penetration process, the goal of this work is to invite solar modellers to consider both processes for a more consistent approach.

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Section: Discussionmentioning

confidence: 99%

Local heating due to convective overshooting and the solar modelling problem

Baraffe

Constantino

Clarke

et al. 2022

A&A

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“…First, while there have been numerical simulations of convection processing a pre-existing magnetic field (Tobias et al 2001;Featherstone et al 2009;Korre et al 2021), we are not aware of any that have studied the extreme aspect ratios (∼ 10 2 ) relevant for subsurface convection zones. The aspect ratio is potentially important because, in order to cause reconnection in large-scale fossil fields, small-scale convective motion has to twist the field over large scales comparable to the stellar radius.…”

Section: Limitationsmentioning

confidence: 99%

Magnetic Archaeology of Early-Type Stellar Dynamos

Jermyn,

Cantiello

2021

Preprint

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Early-type stars show a bimodal distribution of magnetic field strengths, with some showing very strong fields ( 1 kG) and others very weak fields ( 10 G). Recently, we proposed that this reflects the processing or lackthereof of fossil fields by subsurface convection zones. Stars with weak fossil fields process these at the surface into even weaker dynamo-generated fields, while in stars with stronger fossil fields magnetism inhibits convection, allowing the fossil field to remain as-is. We now expand on this theory and explore the time-scales involved in the evolution of near-surface magnetic fields. We find that mass loss strips near-surface regions faster than magnetic fields can diffuse through them. As a result, observations of surface magnetism directly probe the frozen-in remains of the convective dynamo. This explains the slow evolution of magnetism in stars with very weak fields: these dynamogenerated magnetic fields evolve on the time-scale of the mass loss, not that of the dynamo.

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“…A particularly intriguing magnetic effect also occurs in overshooting convection. Magnetic field that exists on much larger scales than the convective turbulence can be expelled from the convective region to form a layer at the edge of the overshoot zone, in a process known generically as "magnetic pumping" (see, e.g., Dorch et al 2001;Tobias et al 1998Tobias et al , 2001Korre et al 2021). There are a number of effects that can contribute to such expulsion but likely the dominant one is the transport of large-scale field down a gradient of turbulent intensity.…”

Section: Introductionmentioning

confidence: 99%

The Rise of Buoyant Magnetic Structures through Convection with a Background Magnetic Field

Manek¹,

Pontin

Brummell³

2022

ApJ

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Inspired by observations of sunspots embedded in active regions, it is often assumed that large-scale, strong magnetic flux emerges from the Sun’s deep interior in the form of arched, cylindrical structures, colloquially known as flux tubes. Here, we continue to examine the different dynamics encountered when these structures are considered as concentrations in a volume-filling magnetic field rather than as isolated entities in a field-free background. Via 2.5D numerical simulations, we consider the buoyant rise of magnetic flux concentrations from a radiative zone through an overshooting convection zone that self-consistently (via magnetic pumping) arranges a volume-filling large-scale background field. This work extends earlier papers that considered the evolution of such structures in a purely adiabatic stratification with an assumed form of the background field. This earlier work established the existence of a bias that created an increased likelihood of the successful rise for magnetic structures with one (relative) orientation of twist and a decreased likelihood for the other. When applied to the solar context, this bias is commensurate with the solar hemispherical helicity rules (SHHRs). This paper establishes the robustness of this selection mechanism in a model incorporating a more realistic background state, consisting of overshooting convection and a turbulently pumped mean magnetic field. Ultimately, convection only weakly influences the selection mechanism, since it is enacted at the initiation of the rise, at the edge of the overshoot zone. Convection does however add another layer of statistical fluctuations to the bias, which we investigate in order to explain variations in the SHHRs.

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On the dynamical interaction between overshooting convection and an underlying dipole magnetic field – I. The non-dynamo regime

Cited by 8 publications

References 42 publications

Local heating due to convective overshooting and the solar modelling problem

Local heating due to convective overshooting and the solar modelling problem

Magnetic Archaeology of Early-Type Stellar Dynamos

The Rise of Buoyant Magnetic Structures through Convection with a Background Magnetic Field

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