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PhD defence

Isotopes and the characterization of extrasolar planets

  • Y. Zhang
Tuesday 6 June 2023
Academy Building
Rapenburg 73
2311 GJ Leiden


  • Prof⁠.dr⁠. I⁠.A⁠.G⁠. Snellen
  • Prof⁠.dr⁠. L⁠. Kreidberg (Max Planck)


Diverse types of exoplanets such as gas giants on close-in orbits (hot Jupiters) and young massive giants on wide orbits (super Jupiters), with no analogs in the Solar System, pose challenges but also opportunities to our understanding of planet formation and evolution. Unravelling the fate of exoplanetary systems is essential for addressing the ultimate question of the origin and the place of our Solar System in the universe. Exoplanet atmospheres with imprints from their history open an important avenue to retrace the origin and evolution of planets. With medium and high-dispersion spectroscopy, we can resolve atomic and molecular spectral features into unique forests of lines that serve as the fingerprints for identifying different species in planetary atmospheres. In this dissertation, I utilize this technique to explore atmospheric compositions, thermal structures, and dynamics of exoplanet atmospheres. I have discovered minor isotopologues in emission spectra of an exoplanet and a brown dwarf for the first time, pioneering the use of carbon isotopic ratios as potential tracers of planet formation. Using high-dispersion transmission spectroscopy, I have investigated the trend of atomic absorption strengths in a sample of ultra-hot Jupiters, which enables disentangling different dynamic regimes of highly-irradiated exoplanets. In addition, I have carried out the first search for helium airglow emission as a probe for atmospheric escape and mass-loss in a hot Jupiter, which will provide insights into the bulk-atmospheric evolution of close-in gaseous planets. These works form the foundation to link spectroscopic observations to planet formation and evolution processes.

PhD dissertations

Approximately one week after the defence, PhD dissertations by Leiden PhD students are available digitally through the Leiden Repository, that offers free access to these PhD dissertations. Please note that in some cases a dissertation may be under embargo temporarily and access to its full-text version will only be granted later.

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