Magnetoconvection in an inclined magnetic field: linear and weakly non-linear models

Thompson, S. D.

doi:10.1111/j.1365-2966.2005.09127.x

Cited by 7 publications

(6 citation statements)

References 31 publications

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“…Such an interaction between a preexisting magnetic field and thermal convection has been studied through numerical simulations mostly in the solar context (see e.g. Hurlburt et al 1996;Cattaneo et al 2003;Proctor 2004;Thomson 2005;Strugarek et al 2011) and in the case of core convection (Featherstone et al 2009). For example, the transition between regimes when the imposed magnetic field is strong (magnetoconvection) and when the magnetic field is weak (dynamo) is investigated (e.g., Cattaneo et al 2003).…”

Section: Discussionmentioning

confidence: 99%

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A dominant magnetic dipole for the evolved Ap star candidate EK Eridani

Aurière¹,

Konstantinova-Antova²,

Petit³

et al. 2011

A&A

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Context. EK Eri is one of the most slowly rotating active giants known, and has been proposed to be the descendant of a strongly magnetic Ap star. Aims. We have performed a spectropolarimetric study of EK Eri over 4 photometric periods with the aim of inferring the topology of its magnetic field. Methods. We used the NARVAL spectropolarimeter at the Bernard Lyot telescope at the Pic du Midi Observatory, along with the leastsquares deconvolution method, to extract high signal-to-noise ratio Stokes V profiles from a timeseries of 28 polarisation spectra. We have derived the surface-averaged longitudinal magnetic field B . We fit the Stokes V profiles with a model of the large-scale magnetic field and obtained Zeeman Doppler images of the surface magnetic strength and geometry. We studied the classical activity indicators, the Ca ii H and K lines, the Ca ii infrared triplet, and Hα line, as well as the stellar radial velocity. Results. B variations of up to about 80 G are observed without any reversal of its sign, and which are in phase with photometric ephemeris. The activity indicators are shown to vary smoothly on a timescale compatible with the rotational period inferred from photometry (308.8 d), however large deviations can occur from one rotation to another. The surface magnetic field variations of EK Eri appear to be dominated by a strong magnetic spot (of negative polarity) which is phased with the dark (cool) photometric spot. Our modeling shows that the large-scale magnetic field of EK Eri is strongly poloidal. For a rotational axis inclination of i = 60• , we obtain a model that is almost purely dipolar. Conclusions. In the dipolar model, the strong magnetic/photometric spot corresponds to the negative pole of the dipole, which could be the remnant of that of an Ap star progenitor of EK Eri. Our observations and modeling conceptually support this hypothesis, suggesting an explanation of the outstanding magnetic properties of EK Eri as the result of interaction between deep convection and the remnant of an Ap star magnetic dipole. Nevertheless, the longitudinal magnetic field curve clearly shows changes from one rotation to the next, indicating that the surface magnetic topology is not static as in an Ap star.

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Section: Discussionmentioning

confidence: 99%

“…They may be associated with flares as observed in active giants (e.g., Konstantinova-Antova et al 2000, 2005. In this case it would be the first time that simultaneous observations of magnetic field and activity indicators have been performed during flares in the stellar context.…”

Section: Discrepant Points In B L and Activity Indicatorsmentioning

confidence: 97%

A dominant magnetic dipole for the evolved Ap star candidate EK Eridani

Aurière¹,

Konstantinova-Antova²,

Petit³

et al. 2011

A&A

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“…Magnetoconvection in a uniform vertical magnetic field is also known to preferentially be oscillatory at onset provided that ζ 1 (e.g., Chandrasekhar 1961;Proctor and Weiss 1982), a phenomenon known as magnetic overstability. This is also possible for non-vertical magnetic fields (e.g., Matthews et al 1992;Hurlburt et al 1996;Thompson 2005, and references therein). Physically, field lines can only be bent significantly by convective motions and act as a spring if they do not slip too much through the moving fluid, which requires, in this context, that the magnetic diffusivity of the fluid be small enough in comparison to its thermal diffusivity.…”

Section: Convection and Magnetic Fieldsmentioning

confidence: 99%

The Sun’s supergranulation

Rincon

Rieutord

2018

Living Rev Sol Phys

110

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Supergranulation is a fluid-dynamical phenomenon taking place in the solar photosphere, primarily detected in the form of a vigorous cellular flow pattern with a typical horizontal scale of approximately 30-35 megameters, a dynamical evolution time of 24-48 h, a strong 300-400 m/s (rms) horizontal flow component and a much weaker 20-30 m/s vertical component. Supergranulation was discovered more than sixty years ago, however, explaining its physical origin and most important observational characteristics has proven extremely challenging ever since, as a result of the intrinsic multiscale, nonlinear dynamical complexity of the problem concurring with strong observational and computational limitations. Key progress on this problem is now taking place with the advent of 21st-century supercomputing resources and the availability of global observations of the dynamics of the solar surface with high spatial and temporal resolutions. This article provides an exhaustive review of observational, numerical and theoretical research on supergranulation, and discusses the current status of our understanding of its origin and dynamics, most importantly in terms of large-scale nonlinear thermal convection, in the light of a selection of recent findings. Keywords Supergranulation · Convection · Turbulence · MHD 4 François Rincon, Michel Rieutord 6 François Rincon, Michel Rieutord

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“…Oscillatory magnetoconvection is also known to occur for non-vertical magnetic fields (e.g., Matthews et al, 1992;Hurlburt et al, 1996;Thompson, 2005, and references therein). Physically, field lines can only be bent significantly by convective motions and act as a spring if they do not slip too much through the moving fluid, which requires, in this context, that the magnetic diffusivity of the fluid be small enough in comparison to its thermal diffusivity.…”

Section: Oscillatory Convection and Magnetic Fieldsmentioning

confidence: 99%

The Sun’s Supergranulation

Rincon

Rieutord

2010

Living Rev. Solar Phys.

165

132

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The Sun's supergranulation refers to a physical pattern covering the surface of the quiet Sun with a typical horizontal scale of approximately 30,000 km and a lifetime of around 1.8 d. Its most noticeable observable signature is as a fluctuating velocity field of 360 m s -1 rms whose components are mostly horizontal. Supergranulation was discovered more than fifty years ago, however explaining why and how it originates still represents one of the main challenges of modern solar physics.A lot of work has been devoted to the subject over the years, but observational constraints, conceptual difficulties and numerical limitations have all concurred to prevent a detailed understanding of the supergranulation phenomenon so far. With the advent of 21st century supercomputing resources and the availability of unprecedented high-resolution observations of the Sun, a stage at which key progress can be made has now been reached. A unifying strategy between observations and modelling is more than ever required for this to be possible.The primary aim of this review is therefore to provide readers with a detailed interdisciplinary description of past and current research on the problem, from the most elaborate observational strategies to recent theoretical and numerical modelling efforts that have all taken up the challenge of uncovering the origins of supergranulation. Throughout the text, we attempt to pick up the most robust findings so far, but we also outline the difficulties, limitations and open questions that the community has been confronted with over the years.In the light of the current understanding of the multiscale dynamics of the quiet photosphere, we finally suggest a tentative picture of supergranulation as a dynamical feature of turbulent magnetohydrodynamic convection in an extended spatial domain, with the aim of stimulating future research and discussions.

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Magnetoconvection in an inclined magnetic field: linear and weakly non-linear models

Cited by 7 publications

References 31 publications

A dominant magnetic dipole for the evolved Ap star candidate EK Eridani

A dominant magnetic dipole for the evolved Ap star candidate EK Eridani

The Sun’s supergranulation

The Sun’s Supergranulation

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