Protosolar D-to-H Abundance and One Part per Billion PH<sub>3</sub> in the Coldest Brown Dwarf

Abstract The coldest Y spectral type brown dwarfs are similar in mass and temperature to cool and warm (∼200–400 K) giant exoplanets. We can therefore use their atmospheres as proxies for planetary atmospheres, testing our understanding of physics and chemistry for these complex, cool worlds. At these cold temperatures, their atmospheres are cold enough for water clouds to form, and chemical timescales increase, increasing the likelihood of disequilibrium chemistry compared to warmer classes of planets. JWST observations are revolutionizing the characterization of these worlds with high signal-to-noise, moderate-resolution near- and mid-infrared spectra. The spectra have been used to measure the abundances of prominent species, like water, methane, and ammonia; species that trace chemical reactions, like carbon monoxide; and even isotopologues of carbon monoxide and ammonia. Here, we present atmospheric retrieval results using both published fixed-slit (Guaranteed Time Observation program 1230) and new averaged time series observations (GO program 2327) of the coldest known Y dwarf, WISE 0855–0714 (using NIRSpec G395M spectra), which has an effective temperature of ∼264 K. We present a detection of deuterium in an atmosphere outside of the solar system via a relative measurement of deuterated methane (CH 3 D) and standard methane. From this, we infer the D/H ratio of a substellar object outside the solar system for the first time. We also present a well-constrained part-per-billion abundance of phosphine (PH 3 ). We discuss our interpretation of these results and the implications for brown dwarf and giant exoplanet formation and evolution.

Authors

Publication Details

Journal
The Astrophysical Journal Letters
Published
2024-12-18
DOI
https://doi.org/10.3847/2041-8213/ad9744
Citations
17
Primary Topic
Stellar, planetary, and galactic studies
Type
article
Field-Weighted Citation Impact
5.64

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article

Protosolar D-to-H Abundance and One Part per Billion PH3 in the Coldest Brown Dwarf

Adam C. Schneider, Melanie J. Rowland, Natasha E. Batalha, James Mang et al.
17 citations
The Astrophysical Journal Letters
Stellar, planetary, and galactic studies
5.64
article

Protosolar D-to-H Abundance and One Part per Billion PH3 in the Coldest Brown Dwarf

Adam C. Schneider, Melanie J. Rowland, Natasha E. Batalha, James Mang, Andrew Skemer, Jacqueline K. Faherty, Richard Freedman, Johanna M. Vos, Ehsan Gharib-Nezhad, Katelyn Allers, Jonathan J. Fortney, Channon Visscher, Mary Anne Limbach, Samuel A. Beiler, Roxana Lupu, Aarynn L. Carter, Ben Burningham, Genaro Suárez, T. R. Geballe, Caroline Morley, G. L. Bjoraker, Dániel Apai, Mark S. Marley, Brittany Miles, Sherelyn Alejandro Merchan, Mikayla J. Wilson, Michael R. Line
article en
17 citations

Abstract

Abstract The coldest Y spectral type brown dwarfs are similar in mass and temperature to cool and warm (∼200–400 K) giant exoplanets. We can therefore use their atmospheres as proxies for planetary atmospheres, testing our understanding of physics and chemistry for these complex, cool worlds. At these cold temperatures, their atmospheres are cold enough for water clouds to form, and chemical timescales increase, increasing the likelihood of disequilibrium chemistry compared to warmer classes of planets. JWST observations are revolutionizing the characterization of these worlds with high signal-to-noise, moderate-resolution near- and mid-infrared spectra. The spectra have been used to measure the abundances of prominent species, like water, methane, and ammonia; species that trace chemical reactions, like carbon monoxide; and even isotopologues of carbon monoxide and ammonia. Here, we present atmospheric retrieval results using both published fixed-slit (Guaranteed Time Observation program 1230) and new averaged time series observations (GO program 2327) of the coldest known Y dwarf, WISE 0855–0714 (using NIRSpec G395M spectra), which has an effective temperature of ∼264 K. We present a detection of deuterium in an atmosphere outside of the solar system via a relative measurement of deuterated methane (CH 3 D) and standard methane. From this, we infer the D/H ratio of a substellar object outside the solar system for the first time. We also present a well-constrained part-per-billion abundance of phosphine (PH 3 ). We discuss our interpretation of these results and the implications for brown dwarf and giant exoplanet formation and evolution.

The Astrophysical Journal LettersVol. 977(2)
National Aeronautics and Space Administration, Alfred P. Sloan Foundation, Space Telescope Science Institute, UK Research and Innovation, Science Foundation Ireland, Science and Technology Facilities Council
Life below water
Openalex Percentile: Top 4%
Stellar, planetary, and galactic studies
5.64
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