The Roasting Marshmallows Program with IGRINS on Gemini South I: Composition and Climate of the Ultra Hot Jupiter WASP-18 b

Abstract

We present high-resolution dayside thermal emission observations of the exoplanet WASP-18b using IGRINS on Gemini South. We remove stellar and telluric signatures using standard algorithms, and we extract the planet signal via cross correlation with model spectra. We detect the atmosphere of WASP-18b at a signal-to-noise ratio (SNR) of 5.9 using a full chemistry model, measure H2O (SNR=3.3), CO (SNR=4.0), and OH (SNR=4.8) individually, and confirm previous claims of a thermal inversion layer. The three species are confidently detected (>4$\sigma$) with a Bayesian inference framework, which we also use to retrieve abundance, temperature, and velocity information. For this ultra-hot Jupiter (UHJ), thermal dissociation processes likely play an important role. Retrieving abundances constant with altitude and allowing the temperature-pressure profile to freely adjust results in a moderately super-stellar carbon to oxygen ratio (C/O=0.75^{+0.14}_{-0.17}) and metallicity ([M/H]=1.03^{+0.65}_{-1.01}). Accounting for undetectable oxygen produced by thermal dissociation leads to C/O=0.45^{+0.08}_{-0.10} and [M/H]=1.17^{+0.66}_{-1.01}. A retrieval that assumes radiative-convective-thermochemical-equilibrium and naturally accounts for thermal dissociation constrains C/O<0.34 (2$\sigma$) and [M/H]=0.48^{+0.33}_{-0.29}, in line with the chemistry of the parent star. Looking at the velocity information, we see a tantalising signature of different Doppler shifts at the level of a few km/s for different molecules, which might probe dynamics as a function of altitude and location on the planet disk. Our results demonstrate that ground-based, high-resolution spectroscopy at infrared wavelengths can provide meaningful constraints on the compositions and climate of highly irradiated planets. This work also elucidates potential pitfalls with commonly employed retrieval assumptions when applied to UHJ spectra.

27 pages, 18 figures, submitted to AAS Journals. Community feedback welcome

References in corpus (26)

• Array Programming with NumPy
• Bayes in the sky: Bayesian inference and model selection in cosmology
• On the radiative equilibrium of irradiated planetary atmospheres
• Mass-Metallicity Trends in Transiting Exoplanets from Atmospheric Abundances of H${}_2$O, Na, and K
• The 2020 release of the ExoMol database: molecular line lists for exoplanet and other hot atmospheres
• A solar C/O and sub-solar metallicity in a hot Jupiter atmosphere
• Five carbon- and nitrogen-bearing species in a hot giant planet's atmosphere
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B
• Theory for the Secondary Eclipse Fluxes, Spectra, Atmospheres, and Light Curves of Transiting Extrasolar Giant Planets
• H2O abundances in the atmospheres of three hot Jupiters
• HELIOS-K 2.0 Opacity Calculator and Open-source Opacity Database for Exoplanetary Atmospheres
• Python Leap Second Management and Implementation of Precise Barycentric Correction (barycorrpy)
• The Impact of Non-Uniform Thermal Structure on the Interpretation of Exoplanet Emission Spectra
• Climate of an Ultra hot Jupiter: Spectroscopic phase curve of WASP-18b with HST/WFC3
• ESPRESSO high resolution transmission spectroscopy of WASP-76b
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• Evidence for a Dayside Thermal Inversion and High Metallicity for the Hot Jupiter WASP-18b
• A unique hot Jupiter spectral sequence with evidence for compositional diversity
• Molecular Cross Sections for High Resolution Spectroscopy of Super Earths, Warm Neptunes and Hot Jupiters
• Detection of Fe and evidence for TiO in the dayside emission spectrum of WASP-33b
• A transition between the hot and the ultra-hot Jupiter atmospheres
• HyDRA-H: Simultaneous Hybrid Retrieval of Exoplanetary Emission Spectra
• Considerations for Atmospheric Retrieval of High-Precision Brown Dwarf Spectra
• Searching for the origin of the Ehrenreich effect in ultra-hot Jupiters: Evidence for strong C/O gradients in the atmosphere of WASP-76b?
• H- and Dissociation in Ultra-hot Jupiters: A Retrieval Case Study of WASP-18b
• Unifying High- and Low-resolution Observations to Constrain the Dayside Atmosphere of KELT-20b/MASCARA-2b

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