Search

Since the release of the first TESS sectors, the high resolution spectrograph CORALIE on the Swiss 1.2 m Euler telescope has observed more than 300 TESSObjects of Interest (TOIs). This work has been conducted in collaboration with the TESS Follow-up Programme to best support exoplanet-observations with largertelescopes, such as HARPS and Espresso. Within a wide range of science cases, we have covered a diverse set of TOIs spanning stellar types, orbital periods andtransit depths.Amongst our sample of TOIs, we find that 43% are still unresolved planet candidates, 26% have been confirmed as planets, 2.5% are brown dwarfs and 20% havebeen identified as eclipsing stellar binaries. We wish to present an overview of the first three years of spectroscopic vetting and follow-up observations. We will also demonstrate our latest data release of spectra, cross-correlation functions and radial velocities, which are publicly available through theDACE platform (dace.unige.ch).

The internal structure of any planet is the result of its composition, radiation environment and age. Exoplanet interiors are hidden worlds that we are offered a glimpse into via the measurements of the most fundamental planet parameters; radius and mass. With this knowledge, we can distinguish rocky Earth-like planets from gaseous giants. We can look for new types of worlds, not represented in our own planetary neighbourhood, and we can ultimately link this diversity of planets to the underlying formation mechanisms. In this thesis, I summarise the exoplanet systems I have detected, confirmed and characterised with transit photometry and radial velocity measurements. They come from a whelm of ground and space-based transit surveys, all focusing on bright stars. I will describe the vetting and screening which lay the foundation for robust detections and stress the importance of identifying false positives.

We report the discovery of a warm Neptune and a hot sub-Neptune transiting TOI-421 (BD-14 1137, TIC 94986319), a bright (V = 9.9) G9 dwarf star in a visual binary system observed by the Transiting Exoplanet Survey Satellite (TESS) space mission in Sectors 5 and 6. We performed ground-based follow-up observations—comprised of Las Cumbres Observatory Global Telescope transit photometry, NIRC2 adaptive optics imaging, and FIbre-fed Echellé Spectrograph, CORALIE, High Accuracy Radial velocity Planet Searcher, High Resolution Échelle Spectrometer, and Planet Finder Spectrograph high-precision Doppler measurements—and confirmed the planetary nature of the 16 day transiting candidate announced by the TESS team. We discovered an additional radial velocity signal with a period of five days induced by the presence of a second planet in the system, which we also found to transit its host star. We found that the inner mini-Neptune, TOI-421 b, has an orbital period of Pb = 5.19672 ± 0.00049 days, a mass of Mb = 7.17 ± 0.66 M⊕, and a radius of Rb = ${2.68}_{-0.18}^{+0.19}$ R⊕, whereas the outer warm Neptune, TOI-421 c, has a period of Pc = 16.06819 ± 0.00035 days, a mass of Mc = ${16.42}_{-1.04}^{+1.06}$ M⊕, a radius of Rc = ${5.09}_{-0.15}^{+0.16}$ R⊕, and a density of ρc = ${0.685}_{-0.072}^{+0.080}$ g cm-3. With its characteristics, the outer planet (ρc = ${0.685}_{-0.072}^{+0.080}$ g cm-3) is placed in the intriguing class of the super-puffy mini-Neptunes. TOI-421 b and TOI-421 c are found to be well-suited for atmospheric characterization. Our atmospheric simulations predict significant Lyα transit absorption, due to strong hydrogen escape in both planets, as well as the presence of detectable CH4 in the atmosphere of TOI-421 c if equilibrium chemistry is assumed. * Based on observations made with ESO Telescopes at the La Silla Observatory under programs ID 1102.C-0923, 0103.C-0874, 0103.C-0759, 0103.C-0442, and 60.A-970. Based on observations obtained with the Nordic Optical Telescope (NOT), operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos (ORM) of the Instituto de Astrofísica de Canarias (IAC). This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. This work makes use of observations from the LCOGT network.