Searches for Stellar Radio Activity in Circular Polarisation

Abstract

Transient radio bursts produced in the coronae of stellar atmospheres and within

planetary magnetospheres often feature a high degree of circular polarisation. These

events reveal the presence of strong magnetic fields, and trace particle accelera-

tion driven by magnetic reconnection, space weather, and auroral current systems.

The detection of stellar radio emission has historically been challenged by the over-

whelmingly higher surface density of extragalactic sources that dominate the radio

sky, which produce a large number of false positive associations to optically identi-

fied stars. Our knowledge of the radio star population has therefore been primarily

driven by targeted study of the most active, nearby systems, impacting the inference

of population statistics and discovery of new regimes of stellar radio activity.

In this thesis I present a body of work that exploits the circular polarisation of

magnetically driven stellar radio emission to identify large samples of radio stars

in widefield surveys. I demonstrate this technique as part of the first

all-sky survey with the Australian Square Kilometre Array Pathfinder (ASKAP)—

the Rapid ASKAP Continuum Survey (RACS). I further extend this search technique to the multi-epoch Variables

and Slow Transients (VAST) pilot survey resulting in 196 detections of a sample

of 46 radio stars, and use the repeat sampling of this group to present constraints

on the statistical fraction of the M-dwarf population that produce radio bursts.

Finally, I describe the use of this technique to discover auroral radio pulses from the

M9.5 ultracool dwarf SCR J1845−6357—the oldest and slowest rotator among radio

detected ultracool dwarfs to date. I conclude

by outlining the application of circular polarisation searches to future surveys with

ASKAP and next generation instruments such as the Square Kilometre Array, which

will result in tens of thousands of new radio star detections and provide a new

window into stellar magnetism.