Thesis Topic: Exoplanet characterisation with optical interferometry

Thesis Supervisors: Antoine Mérand and Sylvestre Lacour


With more than 4000 exoplanets discovered to date, the focus in the field is now shifting from census to characterization by imaging and spectroscopy. The directly imaged exoplanets, seen through thermal emission, offer unique possibilities compared to transit spectroscopy: they are a distinct and young subset of exoplanets at large separations. We propose a PhD thesis centred on high-resolution astrometry and atmospheric spectroscopy of imaged exoplanets, using an observation technique which has only recently been applied to study exoplanets: optical interferometry. Optical interferometry offers much better astrometric accuracy and spectral resolution compared to adaptive optics assisted instrument (GRAVITY Collaboration, A&A 623-L11 2019).

The student will benefit from a large and unique pool of data obtained by an ongoing (2019-2020) large program our team is leading using the GRAVITY instrument at ESO’s Very Large Telescope Interferometer.

Through this program, the student’s goal will be to answer the following two key scientific questions:

• What are the dynamics of directly imaged planetary systems? She/He will monitor the dynamical interactions between seen and unseen companions. We will get the best dynamical masses for directly-imaged planets either in combination with GAIA stellar astrometry or by directly measuring dynamical perturbations caused by planets in resonant multi-planet systems.

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

The candidate will be asked to perform observations at Cerro Paranal in Chile, reduce interferometric data and interpret them using astrometric modelling and exoplanet atmospheres’ models. Skills required will be:

Numerical analysis (essential): the candidate will be expected to develop her/his own tools using the Python language, in addition to existing software 

Soft skills (essential): collaborations will be key in this project, and interaction with various teams will likely be required, such as collaborators, modelling groups, observatory crew, etc.

Instrumentation and optics (preferably): our observations require to push the GRAVITY instrument and VLTI to their limits, hence a deep understanding of optical interferometry facilities and instrumentations will have to be developed.