3D Radiative Transfer for Exoplanet Atmospheres. gCMCRT: A GPU-accelerated MCRT Code

Lee, Elspeth K. H.; Wardenier, Joost P.; Prinoth, Bibiana; Parmentier, Vivien; Grimm, Simon L.; Baeyens, Robin; Carone, L.; Christie, Duncan; Deitrick, Russell; Kitzmann, Daniel; Mayne, Nathan J.; Roman, Michael T.; Thorsbro, B.

doi:10.3847/1538-4357/ac61d6

“…We computed the transmission spectra derived from our photochemical model results using gCMCRT (ref. 40 ) and the ExoAmes high-temperature SO 2 line list 41 . System parameters were taken from ref.…”

Section: Methodsmentioning

confidence: 99%

Photochemically produced SO2 in the atmosphere of WASP-39b

Tsai

¹

,

Lee

²

,

Powell

³

et al. 2023

Nature

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Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability1. However, no unambiguous photochemical products have been detected in exoplanet atmospheres so far. Recent observations from the JWST Transiting Exoplanet Community Early Release Science Program2,3 found a spectral absorption feature at 4.05 μm arising from sulfur dioxide (SO2) in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28 MJ) gas giant exoplanet orbiting a Sun-like star with an equilibrium temperature of around 1,100 K (ref. 4). The most plausible way of generating SO2 in such an atmosphere is through photochemical processes5,6. Here we show that the SO2 distribution computed by a suite of photochemical models robustly explains the 4.05-μm spectral feature identified by JWST transmission observations7 with NIRSpec PRISM (2.7σ)8 and G395H (4.5σ)9. SO2 is produced by successive oxidation of sulfur radicals freed when hydrogen sulfide (H2S) is destroyed. The sensitivity of the SO2 feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an inferred metallicity of about 10× solar. We further point out that SO2 also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations.

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“…If one adopts the Eddington approximation, the proposed methods to solve the spherical RTE usually add more equations to find a converged relationship among J, H, and K (e.g., Hummer & Rybicki 1971;Simonneau 1976;Unno & Kondo 1976). The accurate solution for the spherical, extended atmosphere requires a full 3D RTE solver such as a Monte Carlo RT solver (e.g., Lucy 1999;Lee et al 2022).…”

Section: Conclusion and Discussionmentioning

confidence: 99%

The Inhomogeneity Effect. III. Weather Impacts on the Heat Flow of Hot Jupiters

Zhang,

Li,

Ge

et al. 2023

ApJ

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The interior flux of a giant planet impacts atmospheric motion, and the atmosphere dictates the interior’s cooling. Here we use a non-hydrostatic general circulation model (Simulating Non-hydrostatic Atmospheres on Planets) coupled with a multi-stream multi-scattering radiative module (High-performance Atmospheric Radiation Package) to simulate the weather impacts on the heat flow of hot Jupiters. We found that the vertical heat flux is primarily transported by convection in the lower atmosphere and regulated by dynamics and radiation in the overlying radiation-circulation zone. The temperature inversion occurs on the dayside and reduces the upward radiative flux. The atmospheric dynamics relay the vertical heat transport until the radiation becomes efficient in the upper atmosphere. The cooling flux increases with atmospheric drag due to increased day–night contrast and spatial inhomogeneity. The temperature dependence of the infrared opacity greatly amplifies the opacity inhomogeneity. Although atmospheric circulation could transport heat downward in a narrow region above the radiative-convective boundary, the opacity inhomogeneity effect overcomes the dynamical effect and leads to a larger overall interior cooling than the local simulations with the same interior entropy and stellar flux. The enhancement depends critically on the equilibrium temperature, drag, and atmospheric opacity. In a strong-drag atmosphere hotter than 1600 K, a significant inhomogeneity effect in three-dimensional (3D) models can boost interior cooling several-fold compared to the 1D radiative-convective equilibrium models. This study confirms the analytical argument of the inhomogeneity effect in the companion papers by Zhang. It highlights the importance of using 3D atmospheric models in understanding the inflation mechanisms of hot Jupiters and giant planet evolution in general.

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“…Integrating the annulus area, weighted by the atmospheric transmission obtained from the 2D disks, then results in the effective planet area as a function of wavelength. We benchmarked our setup with gCMCRT (Lee et al 2022), finding excellent agreement.…”

Section: D Transmission Spectrum Modelmentioning

confidence: 76%

A Formally Motivated Retrieval Framework Applied to the High-resolution Transmission Spectrum of HD 189733 b

Blain,

Sánchez-López,

Mollière

2024

AJ

5

0

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Ground-based high-resolution spectra provide a powerful tool for characterizing exoplanet atmospheres. However, they are greatly hampered by the dominating telluric and stellar lines, which need to be removed prior to any analysis. Such removal techniques (“preparing pipelines”) deform the spectrum; hence, a key point is to account for this process in the forward models used in retrievals. We develop a formal derivation on how to prepare froward models for retrievals, in the case where the telluric and instrumental deformations can be represented as a matrix multiplied element-wise with the data. We also introduce the notion of a “bias pipeline metric,” which can be used to compare the bias potential of preparing pipelines. We use the resulting framework to retrieve simulated observations of 1D and 3D exoplanet atmospheres and to reanalyze high-resolution ( R ≈ 80,400 ) near-infrared (0.96–1.71 μm) CARMENES transit data of HD 189733 b. We compare these results with those obtained from a cross-correlation function analysis. With our fiducial retrieval, we find a blueshift of the absorption features of − 5.51 − 0.53 + 0.66 km s−1. In addition, we retrieve a H2O log10(VMR) of − 2.39 − 0.16 + 0.12 and a temperature of 660 − 11 + 6 K. We are also able to put upper limits for the abundances of CH4, CO, H2S, HCN, and NH3, consistent with a subsolar-metallicity atmosphere enriched in H2O. We retrieve a broadened line shape, consistent with rotation- and wind-induced line broadening. Finally, we find a lower limit for the pressure of an opaque cloud consistent with a clear atmosphere, and we find no evidence for hazes.

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3D Radiative Transfer for Exoplanet Atmospheres. gCMCRT: A GPU-accelerated MCRT Code

Cited by 30 publications

References 140 publications

Photochemically produced SO2 in the atmosphere of WASP-39b

Photochemically produced SO2 in the atmosphere of WASP-39b

The Inhomogeneity Effect. III. Weather Impacts on the Heat Flow of Hot Jupiters

A Formally Motivated Retrieval Framework Applied to the High-resolution Transmission Spectrum of HD 189733 b

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