Abstract:

Stars are known to exhibit a wide variety of magnetic activity.  Presumably, this activity is produced by a hydromagnetic dynamo mechanism operating in the interior of the Star.  The purpose of this study is to investigate how the nature of a Star's magnetic output depends on physical processes which consitute the dynamo mechanism, such as differential rotation and circulation.  The dynamo mechanism has been studied extensively in the context of the Sun.  We take this experience gained from the solar dynamo mechanism and build upon it to do a parameter space study with the idea of establishing scaling laws between various observable physical quantities of Stars.  Such a theoretical study when complemented with observations of stellar magnetic activity may provide insight on how the magnetic dynamo evolves with changing conditions in the interior of a Star, at various phases of a Star's lifetime.
 

Presentation Outline

• Introducing the Dynamo Model in the Context of the Sun

•  Solar Magnetic Cycle
•  Frozen-in Approximation
•  Velocity Fields in the Sun
•  Magnetic Buoyancy
•  Dynamo Model (Part 1)
•  Dynamo Model (Part 2)

• Our Dynamo Model

• Parameter Study in the Context of Stars

 
• Simple Differential Rotation

In order to understand the underlying physics, we first study a simplified rotation profile with radial shear only.
•  Results changing the Meridional Flow Speed
•  Results changing the Shear
•  Results changing the Shear and scaling the Meridional Flow Speed with  the Equatorial Rotation Period

• Solar-like Differential Rotation

Including both latitudinal and radial shear
•  Results changing the Shear
• Interesting behavior obtained with Solar-like Differential Rotation

• Conclusions

• Faster meridional flow speed results in lower magnetic cycle periodicities.

• Faster meridional flow also results in a decrease of cycle amplitude. This happens because the toroidal field belt is sweeped away faster through the generating layer not allowing too much field amplification.

• Cycle amplitude is also seen to increase with faster rotation, this is because the shear scales with the rotation rate.

• Cycle peridiocities do not scale with rotation or shear, unless meridional flow speed is made to scale with rotation. For the latter case, cycle period decreases for faster rotation.

• A wide variety of interesting behavior, for example, chaotic, saturated, one sided amplitude oscillations without change in magnetic polarity, is found for a complicated rotational profile like that of the Sun.

• The last result may imply that the solar cycle with a regular periodic behavior is very special!

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