Instabilities of magnetic flux tubes in a stellar convection zone II. Flux rings outside the equatorial plane

1995 ◽  
Vol 81 (3-4) ◽  
pp. 233-265 ◽  
Author(s):  
A. Ferriz-mas ◽  
M. Schüssler
Keyword(s):  
Magnetic Flux ◽  
Equatorial Plane ◽  
Convection Zone ◽  
Flux Tubes ◽  
Stellar Convection ◽  
Magnetic Flux Tubes ◽  
Zone Ii

scholarly journals Linking Thin Flux Tube MHD Models to Apparent Stellar Surface Activity

2004 ◽  
Vol 219 ◽  
pp. 546-551
Author(s):  
T. Granzer ◽  
K. G. Strassmeier
Keyword(s):  
Magnetic Flux ◽  
Surface Activity ◽  
Flux Tube ◽  
Convection Zone ◽  
Active Regions ◽  
Similar Model ◽  
Flux Tubes ◽  
Stellar Convection ◽  
Magnetic Flux Tubes ◽  
Spot Formation

We model thin magnetic flux tubes as they rise from the bottom of a stellar convection zone to the photosphere. On emergence they form active regions, i.e. star spots. This model was very successfully applied to the solar case, where the simulations where in agreement with the butterfly diagram, Joy's law, and Hale's law. We propose the use of a similar model to describe stellar activity in the more extreme form found on active stars. A comparison between Doppler-images of well-observed pre-MS stars and a theoretically derived probability of star-spot formation as a function of latitude is presented.

scholarly journals The Rise of Kink-Unstable Magnetic Flux Tubes in the Solar Convection Zone

1998 ◽  
Vol 505 (1) ◽  
pp. L59-L63 ◽  
Author(s):  
Y. Fan ◽  
E. G. Zweibel ◽  
M. G. Linton ◽  
G. H. Fisher
Keyword(s):  
Magnetic Flux ◽  
Convection Zone ◽  
Solar Convection Zone ◽  
Flux Tubes ◽  
Solar Convection ◽  
Magnetic Flux Tubes

scholarly journals Flux Tubes and Dynamos

1993 ◽  
Vol 157 ◽  
pp. 27-39
Author(s):  
M. Schüssler
Keyword(s):  
Field Strength ◽  
Magnetic Flux ◽  
Convection Zone ◽  
Source Region ◽  
Mean Field ◽  
Active Regions ◽  
Dynamo Theory ◽  
Flux Tubes ◽  
Magnetic Structures ◽  
Magnetic Flux Tubes

The structure of solar surface magnetic fields, the way they erupt from the the convection zone below, and processes like flux expulsion and fragmentation instabilities support the view that magnetic flux in a stellar convection zone is in an intermittent, fragmented state which can be described as an ensemble of magnetic flux tubes. Depending on size and field strength, the dynamics of magnetic flux tubes can strongly differ from the behavior of a passive, diffuse field which is often assumed in conventional mean-field dynamo theory. Observed properties of active regions like emergence in low latitudes, Hale's polarity rules, tilt angles, and the process of sunspot formation from smaller fragments, together with theoretical considerations of the dynamics of buoyant flux tubes indicate that the magnetic structures which erupt in an emerging active region are not passive to convection and originate in a source region (presumably an overshoot layer below the convection zone proper) with a field strength of at least 105 G, far beyond the equipartition field strength with respect to convective flows. We discuss the consequences of such a situation for dynamo theory of the solar cycle and consider the possibility of dynamo models on the basis of flux tubes. A simple, illustrative example of a flux tube dynamo is presented.

scholarly journals Heating of Stellar Chromospheres and Transition Regions

2004 ◽  
Vol 219 ◽  
pp. 437-448
Author(s):  
Zdzislaw E. Musielak
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Acoustic Waves ◽  
Theoretical Models ◽  
Flux Tubes ◽  
Stellar Convection ◽  
Wave Heating ◽  
Active Stars ◽  
Magnetic Flux Tubes ◽  
Magnetic Waves

To explain the heating of stellar chromospheres and transition regions, two classes of heating mechanisms have been considered: dissipation of acoustic and magnetic waves generated in stellar convection zones; and dissipation of currents generated by photospheric motions of surface magnetic fields. The focus of this paper is on the wave heating mechanisms and on recent results which demonstrate that theoretical models of stellar chromospheres based on the wave heating can explain the “basal flux” and the observed Ca II emission in most stars but cannot account for the observed Mg II emission in active stars. The obtained results clearly show that the base of stellar chromospheres is heated by acoustic waves, the heating of the middle and upper chromospheric layers is dominated by magnetic waves associated with magnetic flux tubes, and that other non-wave heating mechanisms are required to explain the structure of the highest layers of stellar chromospheres and transition regions.

scholarly journals On the Stability of Magnetic Flux Tubes in the Equator of a Star

1993 ◽  
Vol 157 ◽  
pp. 45-48
Author(s):  
A. Ferriz-Mas ◽  
M. Schüssler
Keyword(s):  
Magnetic Field ◽  
Angular Velocity ◽  
Field Strength ◽  
Magnetic Flux ◽  
Magnetic Field Strength ◽  
Equatorial Plane ◽  
Flux Tubes ◽  
Magnetic Flux Tubes ◽  
Rotating Star ◽  
The Stability

We consider the linear stability of a toroidal flux tube lying in the equatorial plane of a differentially rotating star and investigate its dependence on superadiabaticity, magnetic field strength, and gradient of angular velocity.

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