The magnetic field vector of the Sun-as-a-star

Vidotto, A. A.

doi:10.1093/mnras/stw758

Cited by 59 publications

(46 citation statements)

References 45 publications

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“…In the axisymmetric model M4 we don't expect any toroidal field out of the surface because of the boundary conditions. In this case the energy of the magnetic field outside the star is dominated by = 3 and = 5 harmonics which is similar to the Sun (Stenflo & Guedel 1988;Stenflo 2013;Vidotto 2016). The non-axisymmetric dynamo model M5 show the dominance of the mode m=1 and = 1 of the large-scale toroidal magnetic field.…”

Section: And Küker 2006mentioning

confidence: 87%

Non-linear regimes in mean-field full-sphere dynamo

Пипин¹

2016

Mon. Not. R. Astron. Soc.

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The mean-field dynamo model is employed to study the non-linear dynamo regimes in a fully convective star of mass 0.3M rotating with period of 10 days. For the intermediate value of the parameter of the turbulent magnetic Prandl number, P m T = 3 we found the oscillating dynamo regimes with period about 40Yr. The higher P m T results to longer dynamo periods. If the large-scale flows is fixed we find that the dynamo transits from axisymmetric to non-axisymmetric regimes for the overcritical parameter of the αeffect. The change of dynamo regime occurs because of the nonaxisymmetric non-linear α-effect. The situation persists in the fully non-linear dynamo models with regards of the magnetic feedback on the angular momentum balance and the heat transport in the star. It is found that the large-scale magnetic field quenches the latitudinal shear in the bulk of the star. However, the strong radial shear operates in the subsurface layer of the star. In the nonlinear case the profile of the angular velocity inside the star become close to the spherical surfaces. This supports the equator-ward migration of the axisymmetric magnetic field dynamo waves. It was found that, the magnetic configuration of the star dominates by the regular nonaxisymmetric mode m=1, forming Yin Yang magnetic polarity pattern with the strong (>500 G) poloidal magnetic field in polar regions.

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Section: And Küker 2006mentioning

confidence: 87%

Non-linear regimes in mean-field full-sphere dynamo

Пипин¹

2016

Mon. Not. R. Astron. Soc.

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“…2, observations of stellar magnetic fields clearly reveal many more modes such as quadrupole, octupole, etc. More recent studies have thus considered complex, multipolar field geometries (Matt and Pudritz 2008;Cohen et al 2009;Jardine et al 2010;Cohen and Drake 2014;Réville et al 2015a, b;Garraffo et al 2015b;Vidotto 2016). This has lead to new formulations of the spin down torque through stellar wind ).…”

Section: Magnetic Effects On Coronal Activity and Windsmentioning

confidence: 99%

Magnetism, dynamo action and the solar-stellar connection

Brun

Browning

2017

Living Rev Sol Phys

239

182

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The Sun and other stars are magnetic: magnetism pervades their interiors and affects their evolution in a variety of ways. In the Sun, both the fields themselves and their influence on other phenomena can be uncovered in exquisite detail, but these observations sample only a moment in a single star's life. By turning to observations of other stars, and to theory and simulation, we may infer other aspects of the magnetism-e.g., its dependence on stellar age, mass, or rotation rate-that would be invisible from close study of the Sun alone. Here, we review observations and theory of magnetism in the Sun and other stars, with a partial focus on the "Solar-stellar connection": i.e., ways in which studies of other stars have influenced our understanding of the Sun and vice versa. We briefly review techniques by which magnetic fields can be measured (or their presence otherwise inferred) in stars, and then highlight some key observational findings uncovered by such measurements, focusing (in many cases) on those that offer particularly direct constraints on theories of how the fields are built and maintained. We turn then to a discussion of how the fields arise in different objects: first, we summarize some essential elements of convection and dynamo theory, including a very brief discussion of mean-field theory and related concepts. Next we turn to simulations of convection and magnetism in stellar interiors, highlighting both some peculiarities of field generation in different types of stars and some unifying physical processes that likely influence dynamo action in general. We conclude with a brief

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“…which are characterised by α lm , β lm , and γ lm coefficients. A detailed description of how these coefficients are determined given radial, meridional and azimuthal magnetic field components can be found in Vidotto (2016). Equating this surface field with the full magnetic field (Equations 9 and 10) evaluated at r = R ; B(θ, φ) = B(R , θ, φ), gives:…”

Section: Calculating the Helicity Densitymentioning

confidence: 99%

Measuring stellar magnetic helicity density

Lund

Jardine

Lehmann

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Helicity is a fundamental property of a magnetic field but to date it has only been possible to observe its evolution in one star -the Sun. In this paper we provide a simple technique for mapping the large-scale helicity density across the surface of any star using only observable quantities: the poloidal and toroidal magnetic field components (which can be determined from Zeeman-Doppler imaging) and the stellar radius. We use a sample of 51 stars across a mass range of 0.1-1.34 M to show how the helicity density relates to stellar mass, Rossby number, magnetic energy and age. We find that the large-scale helicity density increases with decreasing Rossby number R o , peaking at R o 0.1, with a saturation or decrease below that. For both fully-and partially-convective stars we find that the mean absolute helicity density scales with the mean squared toroidal magnetic flux density according to the power law: | h | ∝ B tor 2 0.86 ± 0.04 . The scatter in this relation is consistent with the variation across a solar cycle, which we compute using simulations and observations across solar cycles 23 and 24 respectively. We find a significant decrease in helicity density with age.

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The magnetic field vector of the Sun-as-a-star

Cited by 59 publications

References 45 publications

Non-linear regimes in mean-field full-sphere dynamo

Non-linear regimes in mean-field full-sphere dynamo

Magnetism, dynamo action and the solar-stellar connection

Measuring stellar magnetic helicity density

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