The role of magnetic cycles in the formation of slingshot prominences

Abstract

Slingshot prominences have been observed on rapidly-rotating cool stars. When they are ejected from a star they carry away mass and angular momentum, and so are important in stellar evolution and spin-down. The observed range of slingshot prominence masses vary by over an order of magnitude. The rate at which prominences form, and the masses that they support, depend on the stellar magnetic field. Several stars have been found to have magnetic cycles with observed dipole reversals similar to the solar magnetic field. This thesis aims to study prominence formation for a range of magnetic cycles and how stellar mass-loss rates are affected. In doing so, this work hopes to contribute to the understanding of variable stellar mass-loss rates and their roles in the evolution of rapidly rotating stars.

I used solar magnetograms covering the span of one magnetic cycle to simulate the prominence formation for a young solar-type star. In doing so, the variance of prominence masses and locations are found to be the result of interplay between field strength and the number of stable equilibrium points within the coronal field. Therefore, the total prominence masses and mass-loss rates vary with the magnetic cycle. Expanding this analysis by using simulated magnetograms to create different magnetic cycles, I calculate the total prominence masses for each of the cycle types. I use a flux transport model to create series of magnetograms for four classes of magnetic cycle and identify the similarities and differences in the prominence distributions. I explain the cycle characteristics and prominence distributions in terms of magnetic field strength, topology, and resolution.

This work has implications for characterising magnetic cycles across a range of spectral types, as the variability in prominence formation rates could be an observable link between stellar types and magnetic cycle types. Furthermore, given the potential for prominence ejections to affect planetary atmospheres, the results in this thesis may serve to inform studies on exoplanet habitability by improving our understanding of stellar space-weather.

Date of Award	30 Jun 2025
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Moira Mary Jardine (Supervisor)