JWST is opening many avenues for exploration. For cold brown dwarfs and exoplanets, JWST has opened the door to the mid-infrared wavelength region, where such objects emit significant energy.
For the first time, astronomers have access to mid-infrared spectroscopy for objects colder than 600 K. The first spectra appear to validate the model suite known as ATMO 2020++: atmospheres which include disequilibrium chemistry and have a non-adiabatic pressure-temperature relationship. Preliminary fits to JWST spectroscopy of Y dwarfs show that the slope of the energy distribution from lambda = 4.5 um to lambda = 10 um is very sensitive to gravity.
We explore this phenomenon using PH3-free ATMO 2020++ models and updated WISE W2 – W3 colors. We find that an absolute 4.5 um flux measurement constrains temperature, and the ratio of the 4.5 um flux to the 10 – 15 um flux is sensitive to gravity and less sensitive to metallicity.
We identify 10 T dwarfs with red W2 – W3 colors which are likely to be very low gravity, young, few-Jupiter-mass objects; one of these is the previously known COCONUTS-2b. The unusual Y dwarf WISEPA J182831.08+265037.8 is blue in W2 – W3 and we find that the 4 to 18 um JWST spectrum is well reproduced if the system is a pair of high gravity 400 K dwarfs.
Recently published JWST colors and luminosity-based effective temperatures for late-T and Y dwarfs further corroborate the ATMO 2020++ models, demonstrating the potential for significant improvement in our understanding of cold very low-mass bodies in the solar neighborhood.
S. K. Leggett, Pascal Tremblin
Comments: Accepted for publication in ApJ, 4 November 2024
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2411.03549 [astro-ph.SR] (or arXiv:2411.03549v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2411.03549
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Submission history
From: Sandy Leggett
[v1] Tue, 5 Nov 2024 23:06:53 UTC (666 KB)
https://arxiv.org/abs/2411.03549
Astrobiology
