Prominences : the phantom menace

Abstract

It has been proposed that slingshot prominences may be a mass and angular momentum loss mechanism for rapidly rotating young stars. Stellar evolution models currently rely only on the wind as the angular momentum loss mechanism and do not include prominences. These models often require more angular momentum to be removed than the wind allows, and prominence ejection may hold at least part of the answer. This thesis aims to investigate the locations of prominence formation through mathematical modelling. The magnetic field structures that could support prominences are investigated, typically using two models: a magnetohydrostatic model and a stability method. The distributions of prominences around the star are calculated and, where possible, compared to observations. In some cases the magnetic field of the star is prescribed to be a simple field such as a dipole or quadrupole, and in others the magnetic field is generated from observations of the surface magnetic field, with the coronal magnetic field reconstructed from this, assuming the field is potential. This work finds that prominences can be formed both within the stellar wind of stars, and within the closed field region. With the magnetohydrostatic model, two classes of prominence are found: those close to the surface of the star that could be analogous to solar prominences, and those at very large distances from the stellar surface. Those in the second category may be ejected from the star and act as a mechanism for removing mass and angular momentum. The removal of mass and angular momentum by prominences was modelled using the stable point method, and it was found that for some stars within the sample of M-dwarfs, the prominences could be a significant angular momentum loss mechanism. Work here shows that whilst a tilted dipolar field can typically replicate the locations of observed prominences well, using observed prominence locations to infer the tilt of the dipole is not very effective due to the degeneracy of stable point locations. Overall, prominences are likely to be important contributors to the removal of angular momentum and therefore spin down of a star at certain points in its life, whilst they are typically left out of stellar evolution models. They are likely to be very common across young stars, however they are usually only observable when they transit the stellar disc and therefore they will often be missed by observations due to geometric effects. Those that are observed are likely only being partially observed, meaning that mass predictions from observations are underestimates.