Current Status of Turbulent Dynamo Theory

Brandenburg, Axel; Sokoloff, Dmitry; Subramanian, Kandaswamy

doi:10.1007/s11214-012-9909-x

Cited by 154 publications

(124 citation statements)

References 157 publications

(147 reference statements)

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“…also Lanza 2012) leading to a perturbation of the stellar dynamo. As reviewed by, e.g., Brandenburg et al (2012), the operation of the dynamo in late-type stars implies a mechanism that can get rid of the magnetic helicity that is continuously pumped into the small field scales, otherwise the dynamo is rapidly quenched by magnetohydrodynamic effects. In the Sun, coronal mass ejections associated with large flares are regarded as a viable mechanism for accomplishing this goal, therefore an enhancement of flaring activity in stars with closein companions may help the operation of the dynamo.…”

Section: Discussionmentioning

confidence: 99%

Photospheric activity, rotation, and magnetic interaction in LHS 6343 A

Herrero

Lanza

Ribas

et al. 2013

A&A

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Context. The Kepler mission has recently discovered a brown dwarf companion transiting one member of the M4V+M5V visual binary system LHS 6343 AB with an orbital period of 12.71 days. Aims. The particular interest of this transiting system lies in the synchronicity between the transits of the brown dwarf C component and the main modulation observed in the light curve, which is assumed to be caused by rotating starspots on the A component. We model the activity of this star by deriving maps of the active regions that allow us to study stellar rotation and the possible interaction with the brown dwarf companion.Methods. An average transit profile was derived, and the photometric perturbations due to spots occulted during transits are removed to derive more precise transit parameters. We applied a maximum entropy spot model to fit the out-of-transit optical modulation as observed by Kepler during an uninterrupted interval of ∼500 days. It assumes that stellar active regions consist of cool spots and bright faculae whose visibility is modulated by stellar rotation. Results. Thanks to the extended photometric time series, we refine the determination of the transit parameters and find evidence of spots that are occulted by the brown dwarf during its transits. The modelling of the out-of-transit light curve of LHS 6343 A reveals several starspots rotating with a slightly longer period than the orbital period of the brown dwarf, i.e., 13.13 ± 0.02 days. No signature attributable to differential rotation is observed. We find evidence of a persistent active longitude on the M dwarf preceding the subcompanion point by ∼100 • and lasting for at least ∼500 days. This can be relevant for understanding how magnetic interaction works in low-mass binary and star-planet systems.

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Section: Discussionmentioning

confidence: 99%

Photospheric activity, rotation, and magnetic interaction in LHS 6343 A

Herrero

Lanza

Ribas

et al. 2013

A&A

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“…Turbulent dynamos are generally subdivided into large-scale dynamos and small-scale or fluctuation dynamos depending on whether magnetic fields are amplified on scales smaller or larger than turbulence outer scales, respectively (e.g., Brandenburg et al 2012;Beresniak 2012).…”

Section: Turbulent Dynamosmentioning

confidence: 99%

“…Brandenburg et al 2012). The ratio between both the injection and the dissipation scales can be quantified by the Reynolds number.…”

Section: Introductionmentioning

confidence: 99%

“…There are several recent excellent reviews both on dynamos (see e.g., Brandenburg & Subramanian 2005;Schekochihin et al 2004;Schekochihin et al 2007;Brandenburg et al 2012;Beresniak 2012) and on MHD turbulence theory (e.g., Eyink 2011;Verma 2004;Eyink et al 2011;Lazarian 2011, see also B. Burkhart these Proceedings; to mention just a few). In this lecture we will first present a very brief summary of turbulent dynamo theories, then will focus on small scale turbulent dynamos and their role on the origin and maintenance of magnetic fields in the intra-cluster media.…”

Section: Introductionmentioning

confidence: 99%

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Turbulence and dynamo interlinks

et al. 2012

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Abstract. The role of turbulence in astrophysical environments and its interplay with magnetic fields is still highly debated. In this lecture, we will discuss this issue in the framework of dynamo processes. We will first present a very brief summary of turbulent dynamo theories, then will focus on small scale turbulent dynamos and their particular relevance on the origin and maintenance of magnetic fields in the intra-cluster media (ICM) of galaxies. In these environments, the very low density of the flow requires a collisionless-MHD treatment. We will show the implications of this approach in the turbulent amplification of the magnetic fields in these environments. To finalize, we will also briefly address the connection between MHD turbulence and f ast magnetic reconnection and its possible implications in the diffusion of magnetic flux in the dynamo process.

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“…The thin red and blue lines are the magnetic and kinetic energy spectra for the case of f h = 0. The right panel is a 512 3 simulation from Brandenburg et al (2012) for f h = 1 for unit magnetic Prandtl number. In the right panel, blue indicates kinetic energy spectrum and red indicates magnetic energy spectrum.…”

Section: Large Scale Field Growth: the α 2 Dynamo Examplementioning

confidence: 99%

Magnetic Helicity and Large Scale Magnetic Fields: A Primer

Blackman¹

2016

Space Sciences Series of ISSI

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Magnetic fields of laboratory, planetary, stellar, and galactic plasmas commonly exhibit significant order on large temporal or spatial scales compared to the otherwise random motions within the hosting system. Such ordered fields can be measured in the case of planets, stars, and galaxies, or inferred indirectly by the action of their dynamical influence, such as jets. Whether large scale fields are amplified in situ or a remnant from previous stages of an object's history is often debated for objects without a definitive magnetic activity cycle. Magnetic helicity, a measure of twist and linkage of magnetic field lines, is a unifying tool for understanding large scale field evolution for both mechanisms of origin. Its importance stems from its two basic properties: (1) magnetic helicity is typically better conserved than magnetic energy; and (2) the magnetic energy associated with a fixed amount of magnetic helicity is minimized when the system relaxes this helical structure to the largest scale available. Here I discuss how magnetic helicity has come to help us understand the saturation of and sustenance of large scale dynamos, the need for either local or global helicity fluxes to avoid dynamo quenching, and the associated observational consequences. I also discuss how magnetic helicity acts as a hindrance to turbulent diffusion of large scale fields, and thus a helper for fossil remnant large scale field origin models in some contexts. I briefly discuss the connection between large scale fields and accretion disk theory as well. The goal here is to provide a conceptual primer to help the reader efficiently penetrate the literature.

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Current Status of Turbulent Dynamo Theory

Cited by 154 publications

References 157 publications

Photospheric activity, rotation, and magnetic interaction in LHS 6343 A

Photospheric activity, rotation, and magnetic interaction in LHS 6343 A

Turbulence and dynamo interlinks

Magnetic Helicity and Large Scale Magnetic Fields: A Primer

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