In this dissertation, I explored the domain of exoplanet detection and characterization around solar-type stars, with a keen interest in the methods of radial velocities and astrometry. The essence of this exploration was to contribute to the development of advanced statistical methods for their detection, enhance our understanding of these companions, and draw insightful conclusions from their system architectures.

In order to obtain an accurate picture of the diversity and characteristics and distributions of exoplanets, we need good and robust detection techniques. These techniques serve as the foundation for drawing meaningful conclusions about their properties and understanding their formation and evolution. I explored advanced statistical tools for the analysis of radial velocity (RV) time series, such as Bayesian Model Comparison through the use of nested sampling algorithms. Furthermore, I contributed to the development of a novel detection criterion, the False Inclusion Probability (FIP), which is a more intuitive and accurate detection metric which minimizes both missed detections and false positives. I conducted a rigorous analysis of RV data from the HARPS spectrograph for five systems, uncovering 12 planetary companions falling within the mass range of super-Earths and mini-Neptunes. I also explored the possible formation scenarios for two of these systems using the Bern synthetic planet population. These findings added to the growing list of systems housing inner super-Earths without outer giants.

As a member of the exoplanet team in the Gaia Data Processing and Analysis Consortium, I made significant contributions to the validation of substellar companion detections through astrometry. I then performed a combined analysis of substellar companions using radial velocities and Gaia DR3 derived orbital solutions to determine their true masses. This allowed us to unveil the true nature of brown dwarf and planetary companion candidates that turned out to be stars on low orbital inclinations, and thus refine our estimate on the occurrence rate of brown dwarf companions on close orbits (<10AU) around solar-type stars.

Lastly, I investigated the relationship between the presence of an outer giant and the formation of close-in super-Earths. I present an observing program using the HARPS spectrograph to study the inner regions of stars known to harbor an outer giant. Early findings from this survey have already revealed three planets with short orbital periods below 6 days.

Title	Published in	Access level	OA Policy	Year	Views	Downloads

Exploring the Architectures of Solar-Type Star Planetary Systems with Radial Velocities & Astrometry Using Advanced Statistical Methods				2023	77	17

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Unger, Nicolas

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