The First JWST Spectral Energy Distribution of a Y Dwarf

Abstract

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 /Δ λ ∼100) spectroscopy from 1–12 μ m and three photometric points at 15, 18, and 21 μ m. The spectrum exhibits numerous fundamental, overtone, and combination rotational–vibrational bands of H _2 O, CH _4 , CO, CO _2 , and NH _3 , including the previously unidentified ν _3 band of NH _3 at 3 μ m. Using a Rayleigh–Jeans tail to account for the flux emerging at wavelengths greater than 21 μ m, we measure a bolometric luminosity of 1.523 ± 0.090 × 10 ^20 W. We determine a semiempirical effective temperature estimate of ${467}_{-18}^{+16}$ 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 T _eff = 450 K, log g = 3.25 [cm s ^−2 ], and [M/H] = −0.3. However, the low surface gravity implies an extremely low mass of 1 M _Jup and a very young age of 20 Myr, the latter of which is inconsistent with simulations of volume-limited samples of cool brown dwarfs.

Keywords

• Brown dwarfs
• Stellar effective temperatures
• Y dwarfs
• Near infrared astronomy
• Spectroscopy