Abstract
ABSTRACT Ultra-hot Jupiters are tidally locked gas giants with dayside temperatures high enough to dissociate hydrogen and other molecules. Their atmospheres are vastly non-uniform in terms of chemistry, temperature, and dynamics, and this makes their high-resolution transmission spectra and cross-correlation signal difficult to interpret. In this work, we use the SPARC/MITgcm global circulation model to simulate the atmosphere of the ultra-hot Jupiter WASP-76b under different conditions, such as atmospheric drag and the absence of TiO and VO. We then employ a 3D Monte Carlo radiative transfer code, hires-mcrt, to self-consistently model high-resolution transmission spectra with iron (Fe i) lines at different phases during the transit. To untangle the structure of the resulting cross-correlation map, we decompose the limb of the planet into four sectors, and we analyse each of their contributions separately. Our experiments demonstrate that the cross-correlation signal of an ultra-hot Jupiter is primarily driven by its temperature structure, rotation, and dynamics, while being less sensitive to the precise distribution of iron across the atmosphere. We also show that the previously published iron signal of WASP-76b can be reproduced by a model featuring iron condensation on the leading limb. Alternatively, the signal may be explained by a substantial temperature asymmetry between the trailing and leading limb, where iron condensation is not strictly required to match the data. Finally, we compute the Kp–Vsys maps of the simulated WASP-76b atmospheres, and we show that rotation and dynamics can lead to multiple peaks that are displaced from zero in the planetary rest frame.
Highlights
One of the main goals associated with the characterization of exoplanets is to quantify the abundances of chemical species in their atmospheres
The model solves the primitive equations on a cubed-sphere grid and combines 3D atmospheric dynamics with non-grey radiative transfer
The SPARC/MITgcm has been applied to a variety of hot Jupiters (Showman et al 2009, 2015; Fortney et al 2010; Parmentier et al 2013, 2016, 2021; Kataria et al 2015, 2016; Lewis et al 2017; Steinrueck et al 2019, 2021), as well as a number of ultra-hot Jupiters (Parmentier et al 2018; Arcangeli et al 2019; Pluriel et al 2020)
Summary
One of the main goals associated with the characterization of exoplanets is to quantify the abundances of chemical species in their atmospheres. In high resolution, where individual spectral lines are resolved, the problem becomes even more intricate. This is because line shapes, depths and positions depend profoundly on the 3D thermal structure and chemical composition of the planet, as well as its wind profile and rotation (Miller-Ricci Kempton & Rauscher 2012; Showman et al 2013; Kempton et al 2014; Rauscher & Kempton 2014; Zhang et al 2017; Flowers et al 2019; Harada et al 2021; Seidel et al 2020; Beltz et al 2021; Keles 2021). Comparing observational data to the wrong models may lead to wrong con-
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