WISE 0359 Observations

We present the first JWST spectral energy distribution of a Y dwarf. This spectral energy distribution of the Y0 dwarf WISE J035934.06−540154.6 consists of low-resolution (λ/∆λ ∼ 100) spectroscopy from 1–12 μm and three photometric points at 15, 18, and 21 μm. The spectrum exhibits numerous fundamental, overtone, and combination rotational-vibrational bands of H2O, CH4, CO, CO2, and NH3, including the previously unidentified ν3 band of NH3 at 3 μm. Using a Rayleigh-Jeans tail to account for the flux emerging at wavelengths greater than 21 μm, we measure a bolometric luminosity of 1.523 ± 0.090 × 1020 W. We determine a semi-empirical effective temperature estimate of 465+16
−18 K using the bolometric luminosity and evolutionary models to estimate a radius. Finally, we compare the spectrum and photometry to a grid of atmospheric models and find reasonably good agreement with a model having Teff =450 K, log g=3.25 [cm s−2], [M/H]=−0.3. However, the low surface gravity implies an extremely low mass of 1 MJup and a very young age of 20 Myr, the latter of which is inconsistent with simulations of volume-limited samples of cool brown dwarfs.