Magnetic Drag and 3-D Effects in Theoretical High-Resolution Emission Spectra of Ultrahot Jupiters: the Case of WASP-76b

TL;DR

This study models high-resolution emission spectra of ultrahot Jupiters, specifically WASP-76b, revealing how 3D atmospheric structures and magnetic drag influence spectral features and Doppler shifts throughout the planet's orbit.

Contribution

It provides the first detailed 3D spectral predictions for ultrahot Jupiters considering magnetic drag effects, highlighting the importance of phase-dependent analysis.

Findings

Spectra vary significantly with orbital phase, showing emission, absorption, or both.

Doppler shifts differ between spectral features, allowing differentiation.

Using a single spectral template can bias Doppler shift measurements.

Abstract

Ultrahot Jupiters are ideal candidates to explore with high-resolution emission spectra. Detailed theoretical studies are necessary to investigate the range of spectra we can expect to see from these objects throughout their orbit, because of the extreme temperature and chemical longitudinal gradients that exist across day and nightside regions. Using previously published 3D GCM models of WASP-76b with different treatments of magnetic drag, we post-process the 3D atmospheres to generate high-resolution emission spectra for two wavelength ranges and throughout the planet's orbit. We find that the high-resolution emission spectra vary strongly as a function of phase, at times showing emission features, absorption features, or both, which are a direct result of the 3D structure of the planet. At phases exhibiting both emission and absorption features, the Doppler shift differs in direction between the two spectral features, making them differentiable instead of canceling each other out. Through the use of cross-correlation, we find different patterns in net Doppler shift for models with different treatments of drag: the nightside spectra show opposite signs in their Doppler shift, while the dayside phases have a reversal in the trend of net shift with phase. Finally, we caution researchers from using a single spectral template throughout the planet's orbit; this can bias the corresponding net Doppler shift returned, as it can pick up on a bright region on the edge of the planet disk that is highly red- or blue-shifted.