Brown Dwarfs

Methane Emission From a Cool Brown Dwarf

By Keith Cowing
Status Report
April 20, 2024
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Methane Emission From a Cool Brown Dwarf
The contribution functions for W1935 and W2220 maximum likelihood retrieval models. The CH4 emission seen in W1935 originates from pressures shallower than 0.01 bar. — astro-ph.SR

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).

Jacqueline K. Faherty (American Museum of Natural History), Ben Burningham (University of Hertfordshire), Jonathan Gagné (Planétarium Rio Tinto Alcan), Genaro Suárez (American Museum of Natural History), Johanna M. Vos (Trinity College Dublin), Sherelyn Alejandro Merchan (American Museum of Natural History), Caroline V. Morley (University of Texas at Austin), Melanie Rowland (University of Texas at Austin), Brianna Lacy (University of Texas at Austin), Rocio Kiman (California Institute of Technology), Dan Caselden (American Museum of Natural History), J. Davy Kirkpatrick (IPAC), Aaron Meisner (National Optical-Infrared Astronomy Research Laboratory), Adam C. Schneider (United States Naval Observatory), Marc Jason Kuchner (NASA Goddard Space Flight Center), Daniella Carolina Bardalez Gagliuffi (Amherst College), Charles Beichman (IPAC), Peter Eisenhardt (California Institute of Technology), Christopher R. Gelino (IPAC), Ehsan Gharib-Nezhad (NASA Ames Research Center), Eileen Gonzales (San Francisco State University), Federico Marocco (IPAC), Austin James Rothermich (American Museum of Natural History), Niall Whiteford (American Museum of Natural History)

Comments: Accepted in Nature 9 February 2024
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2404.10977 [astro-ph.SR] (or arXiv:2404.10977v1 [astro-ph.SR] for this version)
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From: Jacqueline Faherty
[v1] Wed, 17 Apr 2024 01:17:54 UTC (10,002 KB)


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