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arXiv · 2404.10977

Methane Emission From a Cool Brown Dwarf

Jacqueline K. Faherty·Ben Burningham·Jonathan Gagné·Genaro Suárez·Johanna M. Vos·Sherelyn Alejandro Merchan·Caroline V. Morley·Melanie Rowland·Brianna Lacy·Rocio Kiman·Dan Caselden·J. Davy Kirkpatrick·Aaron Meisner·Adam C. Schneider·Marc Jason Kuchner·Daniella Carolina Bardalez Gagliuffi·Charles Beichman·Peter Eisenhardt·Christopher R. Gelino·Ehsan Gharib-Nezhad·Eileen Gonzales·Federico Marocco·Austin James Rothermich·Niall Whiteford
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Abstract

Beyond our solar system, aurorae have been inferred from radio observations of isolated brown dwarfs (e.g. Hallinan et al. 2006; Kao et al. 2023). Within our solar system, giant planets have auroral emission with signatures across the electromagnetic spectrum including infrared emission of H3+ and methane. Isolated brown dwarfs with auroral signatures in the radio have been searched for corresponding infrared features but have only had null detections (e.g. Gibbs et al. 2022). CWISEP J193518.59-154620.3. (W1935 for short) is an isolated brown dwarf with a temperature of ~482 K. Here we report JWST observations of strong methane emission from W1935 at 3.326 microns. Atmospheric modeling leads us to conclude that a temperature inversion of ~300 K centered at 1-10 millibar replicates the feature. This represents an atmospheric temperature inversion for a Jupiter-like atmosphere without irradiation from a host star. A plausible explanation for the strong inversion is heating by auroral processes, although other internal and/or external dynamical processes cannot be ruled out. The best fit model rules out the contribution of H3+ emission which is prominent in solar system gas giants however this is consistent with rapid destruction of H3+ at the higher pressure where the W1935 emission originates (e.g. Helling et al. 2019).

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Jacqueline K. Faherty, Ben Burningham, Jonathan Gagné, Genaro Suárez, Johanna M. Vos, Sherelyn Alejandro Merchan, Caroline V. Morley, Melanie Rowland, Brianna Lacy, Rocio Kiman, Dan Caselden, J. Davy Kirkpatrick, Aaron Meisner, Adam C. Schneider, Marc Jason Kuchner, Daniella Carolina Bardalez Gagliuffi, Charles Beichman, Peter Eisenhardt, Christopher R. Gelino, Ehsan Gharib-Nezhad, Eileen Gonzales, Federico Marocco, Austin James Rothermich, Niall Whiteford. 2024-04-17. Methane Emission From a Cool Brown Dwarf. https://doi.org/10.1038/s41586-024-07190-w

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