2024RNAAS...8...13L

James Webb Space Telescope (JWST) mid-infrared spectra of cold brown dwarfs (BDs) are becoming available. In Leggett & Tremblin we demonstrated that an ATMO2020++ synthetic spectrum provided an excellent fit to the first published spectrum. Here we show that these models can reproduce the 1-14 μm spectra of BDs with a range of effective temperature: 350 ≤ T_eff K ≤ 500. A grid of these models, which include disequilibrium chemistry and non-adiabatic pressure-temperature profiles, is available. In addition, a number of models without phosphine were calculated, as PH₃ is absent in the JWST data. Two of the six BDs studied are particularly interesting; one appears to be a young low-mass BD, the other is best fit as a binary. More complete analyses will be possible with an extended model grid, and with additional JWST data. The ATMO2020++ models are recommended for analyses of all BD data.