PhD thesis - Characterization of Accretion Processes on Exoplanets

The student will be co-supervised by M. BONNEFOY and C. DOUGADOS at IPAG, a medium size (195 people) laboratory in Grenoble campus. He will work within the framework of the ANR project FRAME coordinated by M. BONNEFOY. FRAME is focused on protoplanet detection and characterization. As such, He/She will be part of vibrant teams of researchers including astronomers expert in star formation and exoplanets. She/He will also collaborate with data scientists and theoreticians of planet accretion in Europe, China, and the US.

It is now well established that planets originate from disks of gas and dust surrounding young stars during the first 10 millions of years (10 Myr). But the physical processes leading to a fully formed planet are yet to be unraveled. The recent direct imaging detection of protoplanets [1] -- exoplanets still in the process of formation -- promises to solve that mystery.
Giant planets are expected to accrete part of their mass from circumplanetary disks. The accretion of the surrounding gas in the disk should happen at supersonic velocities, creating an accretion shock in the planet vicinity and heating the gas to thousands of kelvin. A set of emission lines are produced at the shock front and appear in the protoplanet spectra. Their intensity, velocity profiles, and variability are now predicted by accretion models at uv, optical, and near-infrared wavelengths [20] and provide a means to probe the physical conditions (temperature, density, kinematics) in the shock regions, derive the gas accretion rates, and ultimately to clarify planet formation processes.

Emission lines have been detected on a dozen of young (1–10 Myr) planetary-mass companions [2]. However, the empirical knowledge of the accretion properties remains very slim and so are the constraints on the accretion models. This stems from fortuitous detection and study of these lines. The inventory is therefore far from complete and detailed follow-up observations are yet to be carried out to better characterize the lines properties and learn more on the accretion processes in the planetary-mass regime.

The PhD project aims to better understand the accretion phenomena ongoing on planetary-mass companions. To do so, the student will analyse data from cutting-edge spectrographs and imagers (VLT/X-SHOOTER, VLT/SINFONI, VLT/MUSE,...) to characterize the emission lines produced by the accretion processes. He/She will conduct a detailed characterization of known accreting objects to derive new information on the accretion physics. She/He will also systematically investigate the occurrence of these lines on the known population of companions. She/He will be given the opportunity to lead his/her own observing programs, and participate in the scientific preparation of ongoing instruments VLT-SPHERE+ and ELT-HARMONI which will soon offer additional opportunities for detecting and characterizing protoplanets.

References:
[1] Haffert et al. 2019, Nature Astronomy, 3, 749
https://arxiv.org/pdf/1906.01486.pdf
[2] Santamaria-Miranda et al. 2018, MNRAS, 475, 2994
https://arxiv.org/pdf/1712.09297.pdf