MIRI-LRS Spectrum of a Cold Exoplanet around a White Dwarf: Water, Ammonia, and Methane Measurements

Abstract The study of the atmosphere of exoplanets orbiting white dwarfs is a largely unexplored field. With WD 0806-661 b, we present the first deep dive into the atmospheric physics and chemistry of a cold exoplanet around a white dwarf. We observed WD 0806-661 b using JWST’s Mid-InfraRed Instrument Low-Resolution Spectrometer, covering the wavelength range from 5 to 12 μ m, and the Imager, providing us with 12.8, 15, 18, and 21 μ m photometric measurements. We carried the data reduction of those data sets, tackling second-order effects to ensure a reliable retrieval analysis. Using the T au RE x retrieval code, we inferred the pressure–temperature structure, atmospheric chemistry, mass, and radius of the planet. The spectrum of WD 0806-661 b is shaped by molecular absorption of water, ammonia, and methane, consistent with a cold Jupiter atmosphere, allowing us to retrieve their abundances. From the mixing ratio of water, ammonia, and methane we derive C/O = 0.34 ± 0.06, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">C</mml:mi> <mml:mo>/</mml:mo> <mml:mi mathvariant="normal">N</mml:mi> <mml:mo>=</mml:mo> <mml:mn>14</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , and N/O = 0.023 ± 0.004 and the ratio of detected metals as a proxy for metallicity. We also derive upper limits for the abundance of CO and CO 2 (1.2 × 10 −6 and 1.6 × 10 −7 , respectively), which were not detected by our retrieval models. While our interpretation of WD 0806-661 b’s atmosphere is mostly consistent with our theoretical understanding, some results—such as the lack of evidence for water clouds, an apparent increase in the mixing ratio of ammonia at low pressure, or the retrieved mass at odds with the supposed age—remain surprising and require follow-up observational and theoretical studies to be confirmed.

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Publication Details

Journal
The Astrophysical Journal Letters
Published
2025-03-25
DOI
https://doi.org/10.3847/2041-8213/adbd46
Citations
8
Primary Topic
Spectroscopy and Laser Applications
Type
article
Field-Weighted Citation Impact
6.05

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article

MIRI-LRS Spectrum of a Cold Exoplanet around a White Dwarf: Water, Ammonia, and Methane Measurements

Sarah Kendrew, Alistair Glasse, M. Guêdel, Adrian M. Glauser et al.
8 citations
The Astrophysical Journal Letters
Spectroscopy and Laser Applications
6.05
article

MIRI-LRS Spectrum of a Cold Exoplanet around a White Dwarf: Water, Ammonia, and Methane Measurements

Sarah Kendrew, Alistair Glasse, M. Guêdel, Adrian M. Glauser, Pascal Tremblin, J. Bouwman, Rens Waters, Göran Östlin, E. F. van Dishoeck, L. Decin, T. P. Ray, Olivier Absil, J. P. Pye, D. Barrado, Polychronis Patapis, Daniel Rouan, Thomas Henning, Quentin Changeat, R. Gastaud, A. Boccaletti, Gillian Wright, Pierre-Olivier Lagage, A. Coulais, Maël Voyer
article en
8 citations

Abstract

Abstract The study of the atmosphere of exoplanets orbiting white dwarfs is a largely unexplored field. With WD 0806-661 b, we present the first deep dive into the atmospheric physics and chemistry of a cold exoplanet around a white dwarf. We observed WD 0806-661 b using JWST’s Mid-InfraRed Instrument Low-Resolution Spectrometer, covering the wavelength range from 5 to 12 μ m, and the Imager, providing us with 12.8, 15, 18, and 21 μ m photometric measurements. We carried the data reduction of those data sets, tackling second-order effects to ensure a reliable retrieval analysis. Using the T au RE x retrieval code, we inferred the pressure–temperature structure, atmospheric chemistry, mass, and radius of the planet. The spectrum of WD 0806-661 b is shaped by molecular absorption of water, ammonia, and methane, consistent with a cold Jupiter atmosphere, allowing us to retrieve their abundances. From the mixing ratio of water, ammonia, and methane we derive C/O = 0.34 ± 0.06, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">C</mml:mi> <mml:mo>/</mml:mo> <mml:mi mathvariant="normal">N</mml:mi> <mml:mo>=</mml:mo> <mml:mn>14</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , and N/O = 0.023 ± 0.004 and the ratio of detected metals as a proxy for metallicity. We also derive upper limits for the abundance of CO and CO 2 (1.2 × 10 −6 and 1.6 × 10 −7 , respectively), which were not detected by our retrieval models. While our interpretation of WD 0806-661 b’s atmosphere is mostly consistent with our theoretical understanding, some results—such as the lack of evidence for water clouds, an apparent increase in the mixing ratio of ammonia at low pressure, or the retrieved mass at odds with the supposed age—remain surprising and require follow-up observational and theoretical studies to be confirmed.

The Astrophysical Journal LettersVol. 982(2)
Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Observatoire de Paris (FR), CEA Grenoble (FR), Astrophysique, Instrumentation et Modélisation (FR), Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères (FR), CEA Cadarache (FR), Laboratoire d’études spatiales et d’instrumentation en astrophysique (FR), Fonctionnement et Conduite des Systèmes de Culture Tropicaux et Méditerranéens (FR), Maison de la Simulation (FR), CEA Paris-Saclay (FR), Institut de Recherche sur les Lois Fondamentales de l'Univers (FR), LIRA - Laboratoire d'instrumentation et de recherche en astrophysique (FR)
Ministerio de Ciencia e Innovación
Openalex Percentile: Top 3%
Spectroscopy and Laser Applications
6.05
DOIOpen Access PDFOpenAlex
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