From Photons to Worlds: An odyssey in exoplanet detection and characterisation

Licentiate thesis, 2021

Since the first unambiguous detection of a planet around a Sun-like, the interest in the new and exciting field of exoplanets has grown immensely. New and exciting developments are seen at a pace unparalleled for most subfields of astronomy and astrophysics.

In this thesis, I describe the two most successful techniques for exoplanet detection and characterisation - transits and radial velocities - and the challenges commonly encountered in extracting the planets from the data.

Transit photometry allows us to measure the planet radius, while radial velocity measurements give us the planet's minimum mass.
These methods' true strength, however, manifests in their combination as it allows us to estimate the true mass, which together with the radius gives us an estimate of a planet's bulk density. This is a powerful quantity, which allows us to speculate about the structure and composition of a planet's interior and atmosphere.

I describe the process of detecting a planet in a stellar light curve, and how transits and radial velocities are modelled together in order to determine the planet parameters. I demonstrate how the ideal theoretical approach can be used to study a system in practice. However, the current challenges in exoplanet characterisation surpass the ideal case, leading us to explore more complex models. Finally, I show how by extending the ideal planet approach with non-parametric models, we can detect planets in complicated datasets, as demonstrated by the case of the TOI-1260 multi-planet system.