Magnetic support of stellar slingshot prominences

Abstract

We present models for the magnetic support of the ‘slingshot prominences’ observed in the coronae of rapidly rotating stars. We calculate mechanical equilibria of loops in a spherical geometry. Prominence-forming loops are found first for dipolar and quadrupolar stellar fields that are fully closed. Equilibria are then found within the stellar wind for a dipolar field that becomes open beyond a given radius. We identify two physical processes that may produce gaps in the distribution of prominence heights: the location of this opening radius, and the behaviour of the buoyancy force. The buoyancy may differ from one prominence-bearing loop to another if they are at different temperatures, thus potentially smearing out any gap in observed height distributions. We produce synthetic prominence distributions and compare to the observations of two well-observed stars: AB Doradus and Speedy Mic. The model recovers the more compact prominence distribution observed for Speedy Mic and reproduces better the overall shape of the height distributions for both stars when the opening radius is beyond the co-rotation radius.