Forward and Inverse Modeling of the Emission and Transmission Spectrum of Gj 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds

Morley, Caroline; Knutson, Heather A.; Line, Michael R.; Fortney, Jonathan J.; Thorngren, Daniel; Marley, Mark S.; Teal, D. J.; Lupu, Roxana

doi:10.3847/1538-3881/153/2/86

Cited by 151 publications

(196 citation statements)

References 92 publications

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“…Both CO and CO 2 have absorption bands in the 4.5 μm Spitzer bandpass; increasing their abundance will accordingly decrease the planet's brightness in this band relative to the 3.6 μm band. Previous models for GJ 436b (Moses et al 2013;Morley et al 2017) serve as a useful demonstration of the effect of very high atmospheric metallicities (>-200 300 solar) on the strength of the CO absorption in the 4.5 μm band. On the planet's night side, Figure 8.…”

Section: Constraints On Atmospheric Circulation 431 General Circulmentioning

confidence: 99%

Phase Curves of WASP-33b and HD 149026b and a New Correlation between Phase Curve Offset and Irradiation Temperature

Zhang

Knutson

Kataria

et al. 2018

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141

140

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We present new 3.6 and 4.5 μm Spitzer phase curves for the highly irradiated hot Jupiter WASP-33b and the unusually dense Saturn-mass planet HD 149026b. As part of this analysis, we develop a new variant of pixel-level decorrelation that is effective at removing intrapixel sensitivity variations for long observations (>10 hr) where the position of the star can vary by a significant fraction of a pixel. Using this algorithm, we measure eclipse depths, phase amplitudes, and phase offsets for both planets at 3.6 and 4.5 μm. We use a simple toy model to show that WASP-33b's phase offset, albedo, and heat recirculation efficiency are largely similar to those of other hot Jupiters despite its very high irradiation. On the other hand, our fits for HD 149026b prefer a very high albedo. We also compare our results to predictions from general circulation models, and we find that while neither planet matches the models well, the discrepancies for HD 149026b are especially large. We speculate that this may be related to its high bulk metallicity, which could lead to enhanced atmospheric opacities and the formation of reflective cloud layers in localized regions of the atmosphere. We then place these two planets in a broader context by exploring relationships between the temperatures, albedos, heat transport efficiencies, and phase offsets of all planets with published thermal phase curves. We find a striking relationship between phase offset and irradiation temperature: the former drops with increasing temperature until around 3400 K and rises thereafter. Although some aspects of this trend are mirrored in the circulation models, there are notable differences that provide important clues for future modeling efforts.

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Section: Constraints On Atmospheric Circulation 431 General Circulmentioning

confidence: 99%

Phase Curves of WASP-33b and HD 149026b and a New Correlation between Phase Curve Offset and Irradiation Temperature

Zhang

Knutson

Kataria

et al. 2018

Self Cite

141

140

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“…For the former, ray-tracing simulations need to be implemented, and the latter warrants three-dimensional Monte Carlo techniques. Thus, typical transit tools, which place a strong emphasis on computational efficiency, neglect the physics of refraction or scattering (e.g., Barstow et al 2012;Benneke & Seager 2012;Howe & Burrows 2012;Line et al 2012;Lee et al 2014;Waldmann et al 2015;Morley et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Analytic Scattering and Refraction Models for Exoplanet Transit Spectra

Robinson

Fortney

Hubbard

2017

ApJ

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Observations of exoplanet transit spectra are essential to understanding the physics and chemistry of distant worlds. The effects of opacity sources and many physical processes combine to set the shape of a transit spectrum. Two such key processes-refraction and cloud and/or haze forward-scattering-have seen substantial recent study. However, models of these processes are typically complex, which prevents their incorporation into observational analyses and standard transit spectrum tools. In this work, we develop analytic expressions that allow for the efficient parameterization of forward-scattering and refraction effects in transit spectra. We derive an effective slant optical depth that includes a correction for forward-scattered light, and present an analytic form of this correction. We validate our correction against a full-physics transit spectrum model that includes scattering, and we explore the extent to which the omission of forward-scattering effects may bias models. Also, we verify a common analytic expression for the location of a refractive boundary, which we express in terms of the maximum pressure probed in a transit spectrum. This expression is designed to be easily incorporated into existing tools, and we discuss how the detection of a refractive boundary could help indicate the background atmospheric composition by constraining the bulk refractivity of the atmosphere. Finally, we show that opacity from Rayleigh scattering and collision-induced absorption will outweigh the effects of refraction for Jupiter-like atmospheres whose equilibrium temperatures are above 400-500K.

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“…To determine the information content of an exoplanet atmosphere as a function of its apparent H-magnitude, we first generated forward models of the exoplanet's transmission spectrum assuming solar metallicity, equilibrium chemistry, and an isothermal temperature-pressure profile at the terminator with the CHIMERA radiative transfer free-retrieval code (Line & Yung 2013;Line et al 2013b;Swain et al 2014;Line et al 2014;Kreidberg et al 2015;Morley et al 2016). To simulate a real observation, realistic uncertainties simulated from the radiometric model were added to this forward model by drawing from a Gaussian distribution, assuming neighboring resolution elements have uncorrelated errors (e.g., Kreidberg et al 2014a).…”

Section: Retrieval Of Atmospheric Abundancesmentioning

confidence: 99%

Quantifying the Impact of Spectral Coverage on the Retrieval of Molecular Abundances from Exoplanet Transmission Spectra

Chapman¹,

Zellem²,

Line³

et al. 2017

PASP

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Using forward models for representative exoplanet atmospheres and a radiometric instrument model, we have generated synthetic observational data to explore how well the major C-and O-bearing chemical species (CO, CO 2 , CH 4 , and H 2 O), important for determining atmospheric opacity and radiation balance, can be constrained by transit measurements as a function of spectral wavelength coverage. This work features simulations for a notional transit spectroscopy mission and compares two cases for instrument spectral coverage (wavelength coverage from 0.5−2.5 µm and 0.5−5 µm). The simulation is conducted on a grid with a range of stellar magnitudes and incorporates a full retrieval of atmospheric model parameters. We consider a range of planets from sub-Neptunes to hot Jupiters and include both low and high mean molecular weight atmospheres. We find that including the 2.5-5 µm wavelength range provides a significant improvement in the degree of constraint on the retrieved molecular abundances: up to ∼3 orders of magnitude for a low mean molecular weight atmosphere (µ = 2.3) and up to a factor of ∼6 for a high mean molecular weight atmosphere (µ = 28). These decreased uncertainties imply that broad spectral coverage between the visible and the mid-infrared is an important tool for understanding the chemistry and composition of exoplanet atmospheres. This analysis suggests that the JWST/NIRSpec 0.6−5 µm prism spectroscopy mode, or similar wavelength coverage with possible future missions, will be an important resource for exoplanet atmospheric characterization.

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Forward and Inverse Modeling of the Emission and Transmission Spectrum of Gj 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds

Cited by 151 publications

References 92 publications

Phase Curves of WASP-33b and HD 149026b and a New Correlation between Phase Curve Offset and Irradiation Temperature

Phase Curves of WASP-33b and HD 149026b and a New Correlation between Phase Curve Offset and Irradiation Temperature

Analytic Scattering and Refraction Models for Exoplanet Transit Spectra

Quantifying the Impact of Spectral Coverage on the Retrieval of Molecular Abundances from Exoplanet Transmission Spectra

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