2024ApJ...973..107B

We present infrared spectral energy distributions of 23 late-type T and Y dwarfs obtained with the James Webb Space Telescope. The spectral energy distributions consist of NIRSpec PRISM and MIRI low-resolution spectrometer spectra covering the ∼1-12 μm wavelength range at λ/Δλ ≈ 100 and broadband photometry at 15, 18, and 21 μm. The spectra exhibit absorption features common to these objects including H₂O, CH₄, CO, CO₂, and NH₃. Interestingly, while the spectral morphology changes relatively smoothly with spectral type at λ < 3 μm and λ > 8 μm, it shows no clear trend in the 5 μm region where a large fraction of the flux emerges. The broad-wavelength coverage of the data enables us to compute the first accurate measurements of the bolometric fluxes of cool brown dwarfs. Combining these bolometric fluxes with parallaxes from Spitzer and Hubble Space Telescope, we also obtain the first accurate bolometric luminosities of these cool dwarfs. We then used the Sonora Bobcat solar-metallicity evolutionary models to estimate the radii of the dwarfs, which results in effective temperature estimates ranging from ∼1000 to 350 K with a median uncertainty of ± 20 K, which is nearly an order of magnitude improvement over previous work. We also discuss how various portions of the spectra either do or do not exhibit a clear sequence when ordered by their effective temperatures.