The Roasting Marshmallows Program with IGRINS on Gemini South I: Composition and Climate of the Ultrahot Jupiter WASP-18 b
The Astronomical Journal, vol. 165, pp. 91
Abstract
Abstract We present high-resolution dayside thermal emission observations of the exoplanet WASP-18 b 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-18 b at a signal-to-noise ratio (S/N) of 5.9 using a full chemistry model, measure H2O (S/N = 3.3), CO (S/N = 4.0), and OH (S/N = 4.8) individually, and confirm previous claims of a thermal inversion layer. The three species are confidently detected (>4σ) with a Bayesian inference framework, which we also use to retrieve abundance, temperature, and velocity information. For this ultrahot Jupiter (UHJ), thermal dissociation processes likely play an important role. Retrieving abundances constant with altitude and allowing the temperature–pressure profile to adjust freely results in a moderately super-stellar carbon-to-oxygen ratio (C/O = 0.75 − 0.17 + 0.14 ) and metallicity ([M/H] = 1.03 − 1.01 + 0.65 ). Accounting for undetectable oxygen produced by thermal dissociation leads to C/O = 0.45 − 0.10 + 0.08 and [M/H] = 1.17 − 1.01 + 0.66 . A retrieval that assumes radiative–convective–thermochemical equilibrium and naturally accounts for thermal dissociation constrains C/O < 0.34 (2σ) and [M/H] = 0.48 − 0.29 + 0.33 , in line with the chemistry of the parent star. Looking at the velocity information, we see a tantalizing signature of different Doppler shifts at the level of a few kilometers per second for different molecules, which might probe dynamics as a function of altitude and/or 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 the spectra of UHJs.
Authors 22
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Matteo Brogi corresponding
University of Warwick · Osservatorio Astrofisico di Torino · University of Turin
Affiliation as printed
Department of Physics, University of Warwick, Coventry, CV4 7AL, UK; matteo.brogi@unito.it
Dipartimento di Fisica, Università degli Studi di Torino, viaPietro Giuria 1, I-10125, Torino, Italy
INAF-Osservatorio Astrofisico di Torino, Via Osservatorio 20, I-10025 Pino Torinese, Italy
Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
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Affiliation as printed
Department of Physics, University of Warwick, Coventry, CV4 7AL, UK; matteo.brogi@unito.it
Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
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Affiliation as printed
School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85281, USA
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Leiden University · University of Warwick · Leiden Observatory
Affiliation as printed
Centre for Exoplanets and Habitability, University of Warwick, Coventry, CV4 7AL, UK
Department of Physics, University of Warwick, Coventry, CV4 7AL, UK; matteo.brogi@unito.it
Leiden Observatory, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
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Arcetri Astrophysical Observatory
Affiliation as printed
INAF—Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze, Italy
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University of Maryland, College Park
Affiliation as printed
Department of Astronomy, University of Maryland, 4296 Stadium Drive, College Park, MD 20742, USA
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Affiliation as printed
Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA
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Centre National de la Recherche Scientifique · Université Côte d'Azur · University of Oxford · Lagrange Laboratory · Observatoire de la Côte d’Azur
Affiliation as printed
Atmospheric, Oceanic, and Planetary Physics, Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, OX1 3PU, UK
Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, France
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Affiliation as printed
Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
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The University of Texas at Austin
Affiliation as printed
Department of Astronomy, University of Texas at Austin, 2515 Speedway, Austin, TX, USA
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Affiliation as printed
Department of Earth & Planetary Sciences, McGill University, 3450 rue University, Montréal, QC, H3A 0E8, Canada
Department of Physics, McGill University, 3600 rue University, Montréal, QC, H3A 2T8, Canada
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Affiliation as printed
School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85281, USA
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Affiliation as printed
Atmospheric, Oceanic, and Planetary Physics, Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, OX1 3PU, UK
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Affiliation as printed
Steward Observatory, University of Arizona, Tucson, AZ 85715, USA
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Affiliation as printed
School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85281, USA
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Affiliation as printed
School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85281, USA
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University of California, Santa Cruz
Affiliation as printed
Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
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Affiliation as printed
Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford, OX1 3RH, UK
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The University of Texas at Austin
Affiliation as printed
Department of Astronomy, University of Texas at Austin, 2515 Speedway, Austin, TX 78712, USA
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Affiliation as printed
Department of Physics, McGill University, 3600 rue University, Montréal, QC, H3A 2T8, Canada
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Affiliation as printed
School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85281, USA
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Affiliation as printed
Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
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