Solar and stellar flares and their connection

Doyle, Lauren (2020) Solar and stellar flares and their connection. Doctoral thesis, Northumbria University.

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Abstract

This thesis focuses on bridging the gap between solar and stellar physics through the study
of flares. Solar flares are the most powerful explosions in the solar system and many stellar
flares have been observed to be orders of magnitudes larger. However, is not yet known if
these phenomena are formed through the same physical process. In this thesis we explore their
common origins through a detailed case study of a solar flare and a robust statistical analysis
of stellar flares with bespoke observations. Using data from the Swedish Solar Telescope,
a detailed study of a solar flare associated with a filament eruption and jet was compared
with advanced 3D MHD simulations. This amalgamation of observation and theory allows for
a complete picture of the event including the pre-flare magnetic structure and the resulting
kinematics of the jet post eruption. Overall, this study aims to characterise the physical
environment capturing many evolutionary properties of the event providing a unique perspective
on eruptive phenomena on the Sun.
With regards to stellar flares, observational data from both K2 and TESS are used to conduct
a statistical analysis on flares from both low mass and solar-type stars. As a result of this, no
relationship between the rotational phase of stellar flares and starspots is present. This was
unexpected as there is a well-established relationship between solar flares and sunspots. This
result yields potential implications for how the magnetic field in fully convective low mass stars
is generated. Possibly, this result implies the surface of these stars is more complex than the
Sun. Furthermore, groups of rapidly fast rotating low mass and solar-type stars were discovered
to exhibit very little flaring activity. This is unusual, as rotation is linked to a star’s dynamo
mechanism and so faster rotating stars are expected to show higher levels of activity.
This research has raised new questions surrounding the underpinning mechanisms driving stellar
flares. In an effort to address this the solar 3D MHD simulation is scaled up to replicate flare
energies seen in the observed stellar flares. This comparative analysis allows for the exploration
of the flare mechanism and potential magnetic structure on these stars, which will be a subject
of future research, in order to explain such high energy flares.

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