Diversity of Cold Worlds: A Near Complete Spectral Energy Distribution for 2MASS J04151954-0935066 using JWST

We present the 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 micron) wavelengths, the SED for this substellar atmosphere is constructed from new JWST NIRSpec G395H (R∼2700) and Magellan FIRE echelle (R∼8000) near-infrared spectra, along with MIRI mid-infrared photometry complemented by spectra from Keck I, IRTF, 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 micron respectively, along with the presence of a CO absorption feature detected mainly at ∼ 4.6 micron.

We detect no absorption of near-infrared K I doublets in the R∼8000 FIRE spectra. In the mid-infrared IRS spectrum, we tentatively identify a new CO₂ feature at 14–16 micron. 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.

Sherelyn Alejandro Merchan, Jacqueline K. Faherty, Genaro Suárez, Kelle L. Cruz, Adam J. Burgasser, Jonathan Gagné, Callie E. Hood, Eileen C. Gonzales, Daniella C. Bardalez Gagliuffi, Jolie L’Heureux, Johanna M. Vos, Adam C. Schneider, Aaron M. Meisner, Caroline Morley, J. Davy Kirkpatrick, Federico Marocco, Rocio Kiman, Charles A. Beichman, Ben Burningham, Dan Caselden, Peter R. Eisenhardt, Christopher R. Gelino, Ehsan Gharib-Nezhad, Marc J. Kuchner, Brianna Lacy, Austin Rothermich, Melanie J. Rowland, Niall Whiteford

Comments: 13 pages, 6 figures, 3 tables. Accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2505.24591 [astro-ph.SR] (or arXiv:2505.24591v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2505.24591
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Submission history
From: Sherelyn Alejandro Merchan
[v1] Fri, 30 May 2025 13:40:13 UTC (6,940 KB)
https://arxiv.org/abs/2505.24591
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