The dynamo action for red dwarfs and red giant and supergiant stars

TL;DR

This paper explores a unified dynamo model based on a Torus structure to explain magnetic fields across red dwarfs, giants, and supergiants, highlighting how star size influences magnetic strength and topology.

Contribution

It introduces a scalable dynamo mechanism involving a Torus structure, with new parameters for magnetic field analysis in various stellar types.

Findings

Magnetic field strength correlates with star size.

Single Torus leads to strong, axisymmetric magnetic fields.

Double-Torus can produce complex, evolving magnetic configurations.

Abstract

We investigate the possibility to apply the already suggested by Sarafopoulos (2017, 2019) main concept of dynamo action to red dwarfs and red giant and supergiant stars. Thus, we attempt to establish a unified dynamo action, being potentially at work at widely varying stellar domains. Thus, the powerful, unique and leading entity generating the primary stellar magnetic field remains the so-called Torus structure. Within the Torus the same sign charges are mutually attracted and the Torus could be simulated as a superconductor. An existing gradient of the rotation rate accumulates net charge in the Torus, and the resulting toroidal current becomes the driving source of the magnetic field. In turn, there is a complicated network of secondary interactions that affect and modulate the whole star's magnetic behaviour. Our dynamo action is potentially at work in fully and partly convecting stars. A major finding is that the strength of the magnetic field, for stars of the same spectral type, is essentially controlled by the size of the star; we suggest that, the larger the star, the deeper inward the Torus is formed. The formation of a single Torus is essentially associated with a large-scale strong, poloidal and axisymmetric magnetic field topology, whereas the generation of a weaker multipolar, non-axisymmetric field configuration in rapid evolution can result from a double-Torus structure (like the solar case). The same basic concept is scaled up or down. Moreover, we identify four key parameters associated with the magnetic field of red dwarfs, giants and supergiants: First, the rotation speed; second, the steepness of the radial gradient of the rotation rate in the shear layer; third, the distance of the Torus from the photosphere and fourth, the cross-sectional area of the Torus. The third and fourth key parameters are introduced for the first time.