The Roasting Marshmallows Program with IGRINS on Gemini South. II. WASP-121 b has Superstellar C/O and Refractory-to-volatile Ratios

Abstract A primary goal of exoplanet science is to measure the atmospheric composition of gas giants in order to infer their formation and migration histories. Common diagnostics for planet formation are the atmospheric metallicity ([M/H]) and the carbon-to-oxygen (C/O) ratio as measured through transit or emission spectroscopy. The C/O ratio in particular can be used to approximately place a planet’s initial formation radius from the stellar host, but a given C/O ratio may not be unique to formation location. This degeneracy can be broken by combining measurements of both the C/O ratio and the atmospheric refractory-to-volatile ratio. We report the measurement of both quantities for the atmosphere of the canonical ultrahot Jupiter WASP-121 b using the high-resolution ( R = 45,000) IGRINS instrument on Gemini South. Probing the planet’s direct thermal emission in both pre- and post-secondary eclipse orbital phases, we infer that WASP-121 b has a significantly superstellar C/O ratio of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.70</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.07</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and a moderately superstellar refractory-to-volatile ratio at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>3.83</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.67</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>3.62</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> </mml:math> stellar. This combination is most consistent with formation between the soot line and H 2 O snow line, but we cannot rule out formation between the H 2 O and CO snow lines or beyond the CO snow line. We also measure velocity offsets between H 2 O, CO, and OH, potentially an effect of chemical inhomogeneity on the planet dayside. This study highlights the ability to measure both C/O and refractory-to-volatile ratios via high-resolution spectroscopy in the near-IR H and K bands.

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Publication Details

Journal
The Astronomical Journal
Published
2024-12-01
DOI
https://doi.org/10.3847/1538-3881/ad8574
Citations
19
Primary Topic
Isotope Analysis in Ecology
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article
Field-Weighted Citation Impact
8.72

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article

The Roasting Marshmallows Program with IGRINS on Gemini South. II. WASP-121 b has Superstellar C/O and Refractory-to-volatile Ratios

Arjun B. Savel, Jorge Abril Sánchez, Peter Smith, John D. Monnier et al.
19 citations
The Astronomical Journal
Isotope Analysis in Ecology
8.72
article

The Roasting Marshmallows Program with IGRINS on Gemini South. II. WASP-121 b has Superstellar C/O and Refractory-to-volatile Ratios

Arjun B. Savel, Jorge Abril Sánchez, Peter Smith, John D. Monnier, Lorenzo Pino, Luis Welbanks, Jonathan J. Fortney, Isaac Malsky, Matteo Brogi, Jean-Michel Désert, Jacob L. Bean, Michael R. Meyer, Eliza M.-R. Kempton, Stefan Pelletier, Vatsal Panwar, Vivien Parmentier, Megan Mansfield, Hayley Beltz, Joost P. Wardenier, Emily Rauscher, Michael R. Line, Krishna Kanumalla
article en
19 citations

Abstract

Abstract A primary goal of exoplanet science is to measure the atmospheric composition of gas giants in order to infer their formation and migration histories. Common diagnostics for planet formation are the atmospheric metallicity ([M/H]) and the carbon-to-oxygen (C/O) ratio as measured through transit or emission spectroscopy. The C/O ratio in particular can be used to approximately place a planet’s initial formation radius from the stellar host, but a given C/O ratio may not be unique to formation location. This degeneracy can be broken by combining measurements of both the C/O ratio and the atmospheric refractory-to-volatile ratio. We report the measurement of both quantities for the atmosphere of the canonical ultrahot Jupiter WASP-121 b using the high-resolution ( R = 45,000) IGRINS instrument on Gemini South. Probing the planet’s direct thermal emission in both pre- and post-secondary eclipse orbital phases, we infer that WASP-121 b has a significantly superstellar C/O ratio of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.70</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.07</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and a moderately superstellar refractory-to-volatile ratio at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>3.83</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.67</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>3.62</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> </mml:math> stellar. This combination is most consistent with formation between the soot line and H 2 O snow line, but we cannot rule out formation between the H 2 O and CO snow lines or beyond the CO snow line. We also measure velocity offsets between H 2 O, CO, and OH, potentially an effect of chemical inhomogeneity on the planet dayside. This study highlights the ability to measure both C/O and refractory-to-volatile ratios via high-resolution spectroscopy in the near-IR H and K bands.

The Astronomical JournalVol. 168(6)
University of Geneva (CH), Centre National de la Recherche Scientifique (FR), University of Arizona (US), University of California, Santa Cruz (US), University of Michigan (US), Arcetri Astrophysical Observatory (IT), University of Warwick (GB), University of Chicago (US), Osservatorio Astrofisico di Torino (IT), Observatoire de la Côte d’Azur (FR), University of Turin (IT), Arizona State University (US), University of Maryland, College Park (US), Université de Montréal (CA), University of Amsterdam (NL)
National Science Foundation, National Aeronautics and Space Administration, Arizona State University, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Nuclear Safety and Security Commission, Korea Astronomy and Space Science Institute, Ministério da Ciência, Tecnologia, Inovações e Comunicações, Agencia Nacional de Investigación y Desarrollo, Science and Technology Facilities Council
Life below water
Openalex Percentile: Top 2%
Isotope Analysis in Ecology
8.72
DOIOpen Access PDFOpenAlex
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