Terra hunting

: extreme precision mass-measurements of Earth like worlds

Abstract

With recent developments in technology, instrumental precision is no longer the limiting factor in detecting Earth-analogue exoplanets using the radial velocity (RV) method. Instead, the astrophysical noise caused by stellar activity can mask or, in extreme cases, mimic planetary RV motions. Therefore, this thesis is dedicated to trying to better understanding the impact of stellar activity in order to mitigate its effects on RV measurements and help push detection thresholds towards low-mass/long-period exoplanets such as Earth-analogues.

I first outline the exoplanet discovery process by presenting the discovery of three hot Jupiters by NGTS, as well as updating the parameters for HATS-54b. After this, I present results from the homogeneous characterisation of a stellar sample of bright, solar-type stars in the Northern hemisphere. This work was performed as part of the gr8stars project, which aims to provide a well-characterised stellar sample to enable future long-term RV missions to select the most suitable candidates to follow.

The majority of this thesis focuses on how new stellar activity indicators can be used to better understand and mitigate the impact of stellar activity on RV measurements. Using these indicators in conjunction with conventional activity indicators, it is observed that although all the systems under consideration show an increased level of suppression as they become more active, it does not always result in a net redshift in the RVs. I use a toy model to qualitatively reproduce these observations. Finally, I show how random forests that use both these new indicators alongside conventional indicators can be used to mitigate the impact of stellar activity on RV measurements. Furthermore, I show the potential that these newly derived stellar activity indicators have to disentangle stellar activity from planetary signals.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Ernst de Mooij (Supervisor) & Christopher Watson (Supervisor)