Thesis Topic: Using single mode interferometry to characterize exoplanets


Thesis Supervisor: Antoine Mérand


Optical interferometry is a new tool to study exoplanets. It recently performed the first direct observation of a previously un-seen exoplanet: beta Pictoris c (Nowak et al. 2020Lacour et al. 2021). Pushing forward toward new discoveries, the ExoGRAVITY project is based on an ESO Large Program (ID 1104.C-0651) to survey and find young giant exoplanets located in the range of 0.1” to 2” from their stars. The observations provide astrometric data of unprecedented accuracy, being crucial for refining the orbital parameters of planets and illuminating their dynamical histories. Furthermore, optical interferometry will measure non-Keplerian perturbations due to planet- planet interactions in multi-planet systems and measure dynamical masses. Over time, repeated observations of the exoplanets at medium resolution (R = 500) will provide a catalogue of K-band spectra of unprecedented quality, for a number of exoplanets. The K- band has the unique properties that it contains many molecular signatures (CO, H2O, CH4, CO2). This allows constraining precisely surface gravity, metallicity, and temperature, if used in conjunction with self-consistent models like Exo-REM or petitRADTRANS (e.g. Mollière et al. 2020).

The forthcoming Gaia data release DR3 will provide new candidates for exoplanets observable by optical interferometry. The candidate will participate to the selection of new exoplanets and their observations with GRAVITY. These new detections will allow additional constrain to models of planetary formation.

The scientific goal of this program is to answer the following two key scientific questions: 

  • What are the dynamics of newly directly imaged planetary systems? The student will be monitoring the orbital parameters and dynamical interactions between seen and unseen companions. He/She will also be able to get the best dynamical masses for directly imaged planets either in combination with Gaia stellar astrometry or by directly measuring dynamical perturbations caused by planet-planet interactions in resonant multi-planet systems.

  • How does the carbon-to-oxygen ratio (C/O) vary for these young exoplanets? This ratio will allow to establish, for the first time, correlations between atmospheric composition and planet formation.

The candidate will also have opportunities to participate in the development and commissioning of new observing modes with GRAVITY.