Exploring the 3D structure of ultra-hot Jupiters using ground-based high-resolution spectroscopy

Thesis

Exoplanet atmospheres are three-dimensional by nature. In this thesis, we model high-resolution transmission spectra of ultra-hot Jupiters to study how their 3D atmospheric structure is imprinted on their signals. With orbital periods of less than two days, ultra-hot Jupiters are tidally locked, such that they have a permanent dayside and a permanent nightside. This means that their atmospheres feature extreme spatial variations in temperature, chemical composition, cloud cover, and wind speed. Because high-resolution spectroscopy can resolve individual absorption lines in a spectrum, this observing technique is especially sensitive to these spatial variations. In this work, we employ a 3D Monte-Carlo radiative transfer code (gCMCRT) to simulate phase-dependent spectra based on outputs of global circulation models. The code accounts for Doppler shifts induced by planet rotation and atmospheric dynamics. We apply our framework to the ultra-hot Jupiter WASP-76b, and we demonstrate that the absorption lines of different chemical species are subject to different Doppler shifts. This is due to the unique spatial distributions of atoms and molecules across the atmosphere. In addition, we show that the behaviour of the observed iron absorption signal of WASP-76b can be reproduced by a model with a thermal asymmetry between the morning and evening terminator of the planet. Furthermore, we delve into the concept of opening angles. These quantify how much information a transmission spectrum contains about the atmosphere of a planet in the line-of-sight direction.

Authors: Wardenier, JP

• DOI: 10.5287/ora-2reykvbxb
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: high-resolution spectroscopy; ultra-hot Jupiters; exoplanet atmospheres; 3D radiative transfer
• Subjects: Planetary science; Astronomy; Physics