Weeks, Angharad; (2025) Exoplanet Host stars in the Age of Gaia and Asteroseismology. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

For centuries, humans have wondered whether other stars can host planets as our sun does. Kant was perhaps the first to concretely publish the view that life could exist outside of our own solar system. However, it is clear that the existence of exoplanets has fascinated us for much of human history. Centuries later, we found evidence for the indisputable existence one of these worlds. It is currently believed that most stars in our Milky Way galaxy host at least one exoplanet. In this thesis I present research which aims to better understand the demographics of the ∼ 6000 exoplanets currently known. Understanding the physical characteristics of all of the currently known systems will provide key insight into how they formed, and why there is such diversity in their compositions and architectures, with respect to our solar system. I do so via the properties of their host stars - the suns at the centre of these distant, yet increasingly familiar, systems. I approach this in three ways. Firstly, I apply homogeneous methods to their characterisation, allowing for robust statistical analysis of their indirectly determined parameters. Secondly, I consider their place in the Milky Way Galaxy itself, probing the demography of the current sample as a result of the galactic context of stars and planets. Finally, I apply asteroseismology - the study of ‘star quakes’, to precisely characterise several individual systems, allowing for the most precise ageing possible of these planets. The work presented in this thesis reveals an important fact: ------------------------------------------------ Not only do exoplanet systems change over time, but exoplanets born at different times look different to one another. Exoplanet formation differs with stellar age. This is intrinsically connected to where, and how, their host star was born. ------------------------------------------------ In the era of Gaia and Asteroseismology, it has become evident that cosmic time is indisputably a crucial lens through which to view exoplanets.

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