Exoplanet exploration in the context of the PLATO mission: From detection to population studies

TL;DR

This thesis uses Kepler/K2 and TESS data, along with ground observations, to discover, validate, and characterize exoplanets, providing insights into planet formation, evolution, and star-planet interactions in preparation for the PLATO mission.

Contribution

It presents new exoplanet discoveries, detailed characterizations, and population analyses that enhance understanding of planetary system evolution relevant to the upcoming PLATO mission.

Findings

Discovery and validation of four planets and 14 new candidates.

Identification of low-density super-Earths and star-planet magnetic interactions.

Observation of an over-density of Neptunian planets in specific orbital periods.

Abstract

This thesis constitutes an observational effort to advance our understanding of planet formation and evolution across different regimes. To do so, we exploited Kepler/K2 and TESS data in combination with ground-based observations, serving as a preparation for the PLATO mission. This endeavour led to the discovery and statistical validation of four planets, the confirmation and characterisation of two other planets, the detection of 14 new planet candidates, and the revision of the properties of 25 previously reported planets. Among them, we find TOI-244 b to be a super-Earth with a density below what would be expected for an Earth-like composition, and we thus refer to TOI-244 b as a low-density super-Earth (LDSE). We also confirm the transiting super-Neptune TOI-5005 b. In this system, we find photometric variability that matches the planetary orbital period, suggesting the existence of magnetic star-planet interactions (MSPIs). We also detect similar synchronised signals in the eccentric HD 118203 system, which appear and disappear across different orbits, in agreement with the well-known 'on/off' nature of MSPIs. At a population level, we find that LDSEs tend to be hosted by stars with subsolar metallicities and that the lowest dense LDSEs tend to receive low insolation fluxes. We also identify an over-density of Neptunian planets in orbits corresponding to periods between ~3.2 and 5.7 days, which we refer to as the Neptunian 'ridge'. The 'ridge', coinciding with the orbital range of the hot Jupiter pileup, suggests a common path in the evolution of the closest giant planets. The low-insolation trend of LDSEs suggests that the largest fraction of volatile elements in these planets is directly exposed to the received irradiation from their host stars. Solving these two problems will greatly contribute to completing the full picture of the evolution of planetary systems.