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Abstract

This thesis is dedicated to the discovery and characterisation of exoplanet systems using the radial velocity- and transit methods. This study focuses on the detailed characterization of several Jovian mass planets discovered in warm orbits (P > 10 days) as part of the Warm gIaNts with tEss (WINE) collaboration, which aims to validate exoplanet discoveries made with the Transiting Exoplanet Survey Satellite (TESS). The physical and orbital properties of these exoplanets have significant implications for planet formation- and evolution theories. Within the WINE collaboration, I studied five different exoplanets in four systems, TOI-2373b, TOI-2416b, TOI-2524b as well as TOI- 6695 b and c. The planets have been detected by TESS as candidates and later confirmed by myself and my collaboration with ground- based follow-up observations using the Fiber-fed Extended Range Optical Spectrograph (FEROS). TOI-2373 b, TOI-2416 b and TOI-2524 b orbit G-type solar analog stars on close orbits, with periods shorter than 15 days each, while TOI-6695b and c orbit a late F-type star on wider orbits of ∼ 80 and ∼ 240 days. The planets presented in this thesis mark important discoveries, with TOI-2373b, TOI-2416b and TOI-2524b residing in the transition region between hot and warm Jupiters, TOI-2373 b being the second most massive exoplanet known to orbit a solar analog star and TOI-2524 b having an inflated radius. The pair of planets in the TOI-6695 system is a rare case of two planets with a period ratio of close to 3, that is, close to the 3:1 resonance. Beyond my work with the WINE collaboration, I studied the case of the young T-Tauri star TWHya. In 2008, an exoplanet discovery was presented for TW Hya. The discovery was based on radial veloc- ity observations with FEROS, which revealed a 3.57 day periodicity. Shortly after, this signal was suggested to be caused by a long-lived stellar spot instead of a planet. In this thesis, I present a detailed radial velocity and photometry analysis, including a spot-induced ra- dial velocity model. I found no further evidence for an exoplanet, but instead attribute the radial velocity signal to a large polar spot, fueled by stellar accretion.