Toward the Analysis of JWST Exoplanet Spectra: Identifying Troublesome Model Parameters

Baudino, J. L.; Mollière, P.; Venot, Olivia; Tremblin, Pascal; Bézard, Bruno; Lagage, Pierre-Olivier

doi:10.3847/1538-4357/aa95be

Cited by 84 publications

(119 citation statements)

References 64 publications

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“…In order to understand the underlying reasons for discrepancies between retrieval results from the same data set, and to avoid occurrences of similar problems in the JWST era, a direct comparison of retrieval algorithms is warranted. We note, an equally important investigation of self-consistent 1D forward models (Baudino et al (2017)) found, unsurprisingly, that differences in the opacity source choices/assumptions resulted in the largest model discrepancies.…”

Section: Introductionmentioning

confidence: 80%

A comparison of exoplanet spectroscopic retrieval tools

Barstow

Changeat

Garland

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Over the last several years, spectroscopic observations of transiting exoplanets have begun to uncover information about their atmospheres, including atmospheric composition and indications of the presence of clouds and hazes. Spectral retrieval is the leading technique for interpretation of transmission spectra and is employed by several teams using a variety of forward models and parameter estimation algorithms. However, different model suites have mostly been used in isolation and so it is unknown whether the results from each are comparable. As we approach the launch of the James Webb Space Telescope we anticipate advances in wavelength coverage, precision, and resolution of transit spectroscopic data, so it is important that the tools that will be used to interpret these information rich spectra are validated. To this end, we present an inter-model comparison of three retrieval suites: TauREx , NEME-SIS and CHIMERA. We demonstrate that the forward model spectra are in good agreement (residual deviations on the order of 20−40 ppm), and discuss the results of cross retrievals between the three tools. Generally, the constraints from the crossretrievals are consistent with each other and with input values to within 1σ. However, for high precision scenarios with error envelopes of order 30 ppm, subtle differences in the simulated spectra result in discrepancies between the different retrieval suites, and inaccuracies in retrieved values of several σ. This can be considered analogous to substantial systematic/astrophysical noise in a real observation, or errors/omissions in a forward model such as molecular linelist incompleteness or missing absorbers.

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Section: Introductionmentioning

confidence: 80%

A comparison of exoplanet spectroscopic retrieval tools

Barstow

Changeat

Garland

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…The BV03 profiles used in ATMO are implemented by Baudino et al (2015). Baudino et al (2017) benchmarked the BV03 and A07 alkali broadening schemes in a 1D radiative-convective model showing large uncertainties in the predicted transmission spectra of hot Jupiters and the emission spectra of brown dwarfs. When generating the grid of brown dwarf atmosphere models in this work we found similar uncertainties.…”

Section: Potassium Broadeningmentioning

confidence: 99%

A new set of atmosphere and evolution models for cool T–Y brown dwarfs and giant exoplanets

Phillips

Tremblin

Baraffe

et al. 2020

A&A

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We present a new set of solar metallicity atmosphere and evolutionary models for very cool brown dwarfs and self-luminous giant exoplanets, which we term ATMO 2020. Atmosphere models are generated with our state-of-the-art 1D radiative-convective equilibrium code ATMO, and are used as surface boundary conditions to calculate the interior structure and evolution of 0.001 − 0.075 M objects. Our models include several key improvements to the input physics used in previous models available in the literature. Most notably, the use of a new H-He equation of state including ab initio quantum molecular dynamics calculations has raised the mass by ∼ 1 − 2% at the stellar-substellar boundary and has altered the cooling tracks around the hydrogen and deuterium burning minimum masses. A second key improvement concerns updated molecular opacities in our atmosphere model ATMO, which now contains significantly more line transitions required to accurately capture the opacity in these hot atmospheres. This leads to warmer atmospheric temperature structures, further changing the cooling curves and predicted emission spectra of substellar objects. We present significant improvement for the treatment of the collisionally broadened potassium resonance doublet, and highlight the importance of these lines in shaping the red-optical and near-infrared spectrum of brown dwarfs. We generate three different grids of model simulations, one using equilibrium chemistry and two using non-equilibrium chemistry due to vertical mixing, all three computed self-consistently with the pressure-temperature structure of the atmosphere. We show the impact of vertical mixing on emission spectra and in colourmagnitude diagrams, highlighting how the 3.5 − 5.5 µm flux window can be used to calibrate vertical mixing in cool T-Y spectral type objects.

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“…Since Exo-REM only handles non-irradiated planets, its model data are missing for GJ 436b and WASP-12b. Finally, the abundances of TiO and VO, as used for WASP-12b, are not provided in Baudino et al (2017) and are shown only for HELIOS. ences in the temperature profiles.…”

Section: Wasp-12bmentioning

confidence: 99%

Self-luminous and Irradiated Exoplanetary Atmospheres Explored with HELIOS

et al. 2019

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We present new methodological features and physical ingredients included in the 1D radiative transfer code HELIOS, improving the hemispheric two-stream formalism. We conduct a thorough intercomparison survey with several established forward models, including COOLTLUSTY, PHOENIX, and find satisfactory consistency with their results. Then, we explore the impact of (i) different groups of opacity sources, (ii) a stellar path length adjustment, and (iii) a scattering correction on self-consistently calculated atmospheric temperatures and planetary emission spectra. First, we observe that temperaturepressure (T-P) profiles are very sensitive to the opacities included, with metal oxides, hydrides, the alkali atoms (and ionized hydrogen) playing an important role for the absorption of shortwave radiation (in very hot surroundings). Moreover, if these species are sufficiently abundant, they are likely to induce non-monotonic T-P profiles. Second, without the stellar path length adjustment, the incoming stellar flux is significantly underestimated for zenith angles above 80 • , which somewhat affects the upper atmospheric temperatures and the planetary emission. Third, the scattering correction improves the accuracy of the computation of the reflected stellar light by ∼ 10%. We use HELIOS to calculate a grid of cloud-free atmospheres in radiative-convective equilibrium for self-luminous planets for a range of effective temperatures, surface gravities, metallicities, and C/O ratios, to be used by planetary evolution studies. Furthermore, we calculate dayside temperatures and secondary eclipse spectra for a sample of exoplanets for varying chemistry and heat redistribution. These results may be used to make predictions on the feasibility of atmospheric characterizations with future observations.

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Toward the Analysis of JWST Exoplanet Spectra: Identifying Troublesome Model Parameters

Cited by 84 publications

References 64 publications

A comparison of exoplanet spectroscopic retrieval tools

A comparison of exoplanet spectroscopic retrieval tools

A new set of atmosphere and evolution models for cool T–Y brown dwarfs and giant exoplanets

Self-luminous and Irradiated Exoplanetary Atmospheres Explored with HELIOS

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