Diversity of Cold Worlds: A Near-complete Spectral Energy Distribution for 2MASS J04151954−0935066 Using JWST

We present a near-complete spectral energy distribution (SED) for an extrasolar world: the T8 brown dwarf 2MASS J04151954−0935066. Spanning from optical to mid-infrared (0.7–20.4 μm) wavelengths, the SED for this substellar atmosphere is constructed from new James Webb Space Telescope (JWST) NIRSpec G395H (R ∼ 2700) and Magellan Folded-port InfraRed Echellete (FIRE) echelle (R ∼ 8000) near-infrared spectra, along with MIRI mid-infrared photometry complemented by spectra from Keck I, Infrared Telescope Facility, Magellan, AKARI, Spitzer, and photometry from various surveys and missions. The NIRSpec G395H spectrum reveals strong molecular absorptions from NH3, CH4, H2S, CO2, and H2O at approximately 3.00, 3.35, 3.95, 4.25, and 5.00 μm, respectively, along with the presence of a CO absorption feature detected mainly at ∼4.6 μm. We detect no absorption of near-infrared K i doublets in the R ∼ 8000 FIRE spectra. In the mid-infrared Infrared Spectrograph spectrum, we tentatively identify a new CO2 feature at 14–16 μm. The comprehensive SED allows us to empirically constrain bolometric luminosity, effective temperature, mass, and radius. Additionally, we demonstrate that the NIRSpec G395H resolution, the highest allowable by JWST, enables a precise radial velocity measurement of 47.1 ± 1.8 km s−1 for the object, in agreement with previous measurements.