Abstract
ABSTRACT Thermal dissociation and recombination of molecular hydrogen, H2, in the atmospheres of ultra-hot Jupiters (UHJs) has been shown to play an important role in global heat redistribution. This, in turn, significantly impacts their planetary emission, yet only limited investigations on the atmospheric effects have so far been conducted. Here, we investigate the heat redistribution caused by this dissociation/recombination reaction, alongside feedback mechanisms between the atmospheric chemistry and radiative transfer, for a planetary and stellar configuration typical of UHJs. To do this, we have developed a time-dependent pseudo-2D model, including a treatment of time-independent equilibrium chemical effects. As a result of the reaction heat redistribution, we find temperature changes of up to ∼400 K in the atmosphere. When TiO and VO are additionally considered as opacity sources, these changes in temperature increase to over ∼800 K in some areas. This heat redistribution is found to significantly shift the region of peak atmospheric temperature, or hotspot, towards the evening terminator in both cases. The impact of varying the longitudinal wind speed on the reaction heat redistribution is also investigated. When excluding TiO/VO, increased wind speeds are shown to increase the impact of the reaction heat redistribution up to a threshold wind speed. When including TiO/VO there is no apparent wind speed threshold, due to thermal stabilization by these species. We also construct pseudo-2D phase curves from our model, and highlight both significant spectral flux damping and increased phase offset caused by the reaction heat redistribution.
Highlights
Offering both valuable insight into extreme planetary atmosphericU conditions, and an abundance of available data due to detection biases, the hydrogen-dominated atmospheres of highly irradiated global circulation in the form of strong longitudinal winds, dominated by an equatorial jet, in some cases reaching speeds of over 5 km s−1 (Komacek et al 2017).L ultra-hot Jupiter (UHJ) exoplanets have recently become a focus of both the modelling and observational astrophysics communities.A These planets are broadly assumed to be tidally-locked, due to strong gravitational interactions with their host star, causing huge irradiative disparities between their permanently stellar-facing day-side and much colder night-side
We have developed a time-dependent pseudo-2D model, including a treatment of time-independent equilibrium chemical effects
IG 2.1 Atmosphere model: atmosphere model (ATMO) R The 1D/2D atmosphere code ATMO. This is likely to be a good assumption for the results presented in this paper, since the high-temperatures of the atmospheres that we focus on in this study mean that condensation is expected to be unimportant
Summary
U conditions, and an abundance of available data due to detection biases, the hydrogen-dominated atmospheres of highly irradiated global circulation in the form of strong longitudinal winds, dominated by an equatorial jet, in some cases reaching speeds of over 5 km s−1 (Komacek et al 2017). Incorporated the ability to consistently calculate the temperature profile with non-equilibrium chemistry, including vertical mixing and photochemistry (Drummond et al 2016) These models have since been used to investigate a range of planetary atmospheres, such as hot Neptunes (Agúndez et al 2014b) and brown dwarfs (Phillips et al 2020), but have predominantly been used for hot Jupiters (Moses et al 2013; Goyal et al 2020). The use of 1D models for planets like ultra-hot Jupiters, which display such extreme longitudinal atmospheric change, clearly has significant limitations These models, by design, average incoming stellar flux to a single value, severely limiting their use for any study on effects caused by longitudinal temperature or chemical variations. The model uses the ITcorrelated-k approximation with the method of random overlap to to include a time-dependent pseudo-2D capability We use this to study the effect of H2 thermal dissociation/recombination,.
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