Constraining Hot Jupiter Atmospheric Structure and Dynamics through Doppler-shifted Emission Spectra

Abstract

Abstract We present a coupled 3D atmospheric dynamics and radiative transfer model to predict the disk-integrated thermal emission spectra of transiting exoplanets in edge-on orbits. We calculate spectra at high resolution to examine the extent to which high-resolution emission spectra are influenced by 3D atmospheric dynamics and planetary rotation and to determine whether and how we can constrain thermal structures and atmospheric dynamics through high-resolution spectroscopy. This study represents the first time that the line-of-sight geometry and resulting Doppler shifts from winds and rotation have been treated self-consistently in an emission spectrum radiative transfer model, which allows us to assess the impact of the velocity field on thermal emission spectra. We apply our model to predict emission spectra as a function of orbital phase for three hot Jupiters: HD 209458b, WASP-43b, and HD 189733b. We find net Doppler shifts in modeled spectra due to a combination of winds and rotation at a level of 1–3 km s−1. These Doppler signatures vary in a quasi-sinusoidal pattern over the course of the planets’ orbits as the hot spots approach and recede from the observer’s viewpoint. We predict that WASP-43b produces the largest Doppler shift due to its fast rotation rate. We find that the net Doppler shift in an exoplanet’s disk-integrated thermal emission spectrum results from a complex combination of winds, rotation, and thermal structure. However, we offer a simple method that estimates the magnitude of equatorial wind speeds in hot Jupiters through measurements of net Doppler shifts and lower-resolution thermal phase curves.