The Effect of Magnetic Spots on Stellar Winds and Angular Momentum Loss

Cohen, Ofer; Drake, J. J.; Kashyap, Vinay; Gombosi, T. I.

doi:10.1088/0004-637x/699/2/1501

Cited by 31 publications

(40 citation statements)

References 46 publications

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“…Works including more complex coronal magnetic fields such as the inclusion of magnetic spots (e.g. Cohen et al 2009;Garraffo et al 2015), tilted magnetospheres (e.g. Vidotto et al 2010) and using ZDI observations (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…With the cylindrical extent of the Alfvén surface being directly related to the efficiency of the magnetic braking mechanism, it is this global field strength and geometry that is required to compute accurate braking torques in MHD simulations (Réville et al 2015(Réville et al , 2016. However, the effect of the higher order components on the acceleration of the wind close in to the star may not be non-negligible (Cranmer & Van Ballegooijen 2005;Cohen et al 2009). Additionally, the small scale surface features described by these higher order geometries (e.g.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Effect of Combined Magnetic Geometries on Thermally Driven Winds. II. Dipolar, Quadrupolar, and Octupolar Topologies

Finley

Matt

2018

ApJ

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During the lifetime of sun-like or low mass stars a significant amount of angular momentum is removed through magnetised stellar winds. This process is often assumed to be governed by the dipolar component of the magnetic field. However, observed magnetic fields can host strong quadrupolar and/or octupolar components, which may influence the resulting spin-down torque on the star. In Paper I, we used the MHD code PLUTO to compute steady state solutions for stellar winds containing a mixture of dipole and quadrupole geometries. We showed the combined winds to be more complex than a simple sum of winds with these individual components. This work follows the same method as Paper I, including the octupole geometry which increases the field complexity but also, more fundamentally, looks for the first time at combining the same symmetry family of fields, with the field polarity of the dipole and octupole geometries reversing over the equator (unlike the symmetric quadrupole). We show, as in Paper I, that the lowest order component typically dominates the spin down torque. Specifically, the dipole component is the most significant in governing the spin down torque for mixed geometries and under most conditions for real stars. We present a general torque formulation that includes the effects of complex, mixed fields, which predicts the torque for all the simulations to within 20% precision, and the majority to within ≈ 5%. This can be used as an input for rotational evolution calculations in cases where the individual magnetic components are known.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Effect of Combined Magnetic Geometries on Thermally Driven Winds. II. Dipolar, Quadrupolar, and Octupolar Topologies

Finley

Matt

2018

ApJ

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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

252

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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“…Some authors have studied the influence of the topology of coronal field in the properties of stellar winds and resulting braking torques, but mostly by using simplified configurations (e.g., dipolar versus quadrupolar field, as in Matt & Pudritz 2008). Others have furthermore considered how the presence of strong magnetic spots (localized magnetic flux enhancements) specifically affects the angular momentum-loss rate (e.g., Aibéo et al 2007;Cohen et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Coupling the Solar Dynamo and the Corona: Wind Properties, Mass, and Momentum Losses During an Activity Cycle

Pinto

Brun

Jouve

et al. 2011

ApJ

113

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We study the connections between the Sun's convection zone and the evolution of the solar wind and corona. We let the magnetic fields generated by a 2.5-dimensional (2.5D) axisymmetric kinematic dynamo code (STELEM) evolve in a 2.5D axisymmetric coronal isothermal magnetohydrodynamic code (DIP). The computations cover an 11 year activity cycle. The solar wind's asymptotic velocity varies in latitude and in time in good agreement with the available observations. The magnetic polarity reversal happens at different paces at different coronal heights. Overall the Sun's mass-loss rate, momentum flux, and magnetic braking torque vary considerably throughout the cycle. This cyclic modulation is determined by the latitudinal distribution of the sources of open flux and solar wind and the geometry of the Alfvén surface. Wind sources and braking torque application zones also vary accordingly.

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The Effect of Magnetic Spots on Stellar Winds and Angular Momentum Loss

Cited by 31 publications

References 46 publications

The Effect of Combined Magnetic Geometries on Thermally Driven Winds. II. Dipolar, Quadrupolar, and Octupolar Topologies

The Effect of Combined Magnetic Geometries on Thermally Driven Winds. II. Dipolar, Quadrupolar, and Octupolar Topologies

Magnetism, dynamo action and the solar-stellar connection

Coupling the Solar Dynamo and the Corona: Wind Properties, Mass, and Momentum Losses During an Activity Cycle

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