Into the Storm: Diving into the winds of the ultra hot Jupiter WASP-76 b with HARPS and ESPRESSO

Abstract

Context. Despite swift progress in the characterisation of exoplanet atmospheres in composition and structure, the study of atmospheric dynamics has not progressed at the same speed. While theoretical models have been developed to describe the lower layers of the atmosphere and, disconnected, the exosphere, little is known about the intermediate layers up to the thermosphere. Aims. We aim to provide a clearer picture of atmospheric dynamics for the class of ultra hot Jupiters, highly-irradiated gas giants, on the example of WASP-76 b. Methods. We analysed two datasets jointly, obtained with the HARPS and ESPRESSO spectrographs, to interpret the resolved planetary sodium doublet. We then applied the MERC code, which retrieves wind patterns, speeds, and temperature profiles on the line shape of the sodium doublet. An updated version of MERC, with added planetary rotation, also provides the possibility to model the latitude dependence of the wind patterns. Results. We retrieve the highest Bayesian evidence for an isothermal atmosphere, interpreted as a mean temperature of 3389 ± 227 K, a uniform day-to-night side wind of 5.5 +1.4 −2.0 km s −1 in the lower atmosphere with a vertical wind in the upper atmosphere of 22.7 +4.9 −4.1 km s −1 , switching atmospheric wind patterns at 10 −3 bar above the reference surface pressure (10 bar). Conclusions. Our results for WASP-76 b are compatible with previous studies of the lower atmospheric dynamics of WASP-76 b and other ultra hot Jupiters. They highlight the need for vertical winds in the intermediate atmosphere above the layers probed by global circulation model studies to explain the line broadening of the sodium doublet in this planet. This work demonstrates the capability of exploiting the resolved spectral line shapes to observationally constrain possible wind patterns in exoplanet atmospheres, an invaluable input to more sophisticated 3D atmospheric models in the future.

Mining the Ultra-Hot Skies of HAT-P-70b: Detection of a Profusion of Neutral and Ionized Species

“…We emphasize that, despite the high number of species we detected in HAT-P- 70 b and the remarkable strength of some of them (e.g. Fe II), the work presented here only used a single transit event with HARPS-N -further studies could reveal additional species and allow for a detailed investigation of the atmospheric dynamics of HAT-P-70 b (Wardenier et al 2021;Seidel et al 2021). HAT-P-70 b is also a promising target for emission spectroscopy to investigate the chemistry of its day-side (e.g.…”

An Atomic Spectral Survey of WASP-76b: Resolving Chemical Gradients and Asymmetries

“…We chose to use an isothermal PT profile with a temperature of 3000 K. An isothermal PT profile is often used for transmission spectroscopy as this type of spectrum is not very dependent on the underlying PT profile. Indeed, Seidel et al (2021) found that an isothermal profile fit this ESPRESSO data well and was preferred over the more complex profiles that they tested. A temperature of 3000 K was motivated as an intermediate choice between Landman et al (2021), who retrieved a best-fit temperature of 2701 +448 −279 , and Seidel et al (2021), who found a best-fit temperature of 3389 ± 227 K. Figure 2 shows how changing the temperature changes the resulting model spectrum, and in Section 6.1 we test how our results change if we use isothermal PT profiles of 2000 and 4000 K.…”

“…More information about the reduction procedure and the data can be found in the original publication where the data were presented (Ehrenreich et al 2020). This dataset has also been used in two subsequent papers, Tabernero et al (2021) and Seidel et al (2021). Tabernero et al (2021) identified individual absorption lines from Li I, Na I, Mg I, Ca II, Mn I, K I, and Fe I, and also searched for Fe I, Ti I, Cr I, Ni I, TiO, VO and ZrO using the cross correlation technique, but only detected the previously-seen Fe I signal.…”

“…Tabernero et al (2021) identified individual absorption lines from Li I, Na I, Mg I, Ca II, Mn I, K I, and Fe I, and also searched for Fe I, Ti I, Cr I, Ni I, TiO, VO and ZrO using the cross correlation technique, but only detected the previously-seen Fe I signal. Seidel et al (2021) performed a concentrated analysis of the Na I doublet and found evidence for a uniform dayto-night wind, as well as a vertical wind in the upper atmosphere, which acts to significantly broaden the Na I doublet.…”

“…As WASP-76b transits in front of its host star, its viewing angle changes by φ = 30 • (Ehrenreich et al 2020) and assuming tidal locking, more of the illuminated morningside is visible at the start of the transit, while more of its illuminated eveningside is visible at the end of the transit. Due to the interplay between the planet's rotation and the measured global wind blowing from the hot dayside to the cool nightside (Seidel et al 2021), the eveningside of the planet is expected to have a larger blueshift than the morningside, but this velocity change would only be able to be resolved if the atmospheric temperature profile or abundance of Fe I were not uniform over the surface of the planet. Recent in-depth global circulation modeling (GCM) by Wardenier et al (2021) and Savel et al (2021) confirmed that a hotter evening terminator, a cooler morning terminator, and either condensation of Fe I or clouds obscuring the cooler morningside were necessary to explain the asymmetry.…”