Brown Dwarfs

JWST/NIRSpec Observations Of The Coldest Known Brown Dwarf

By Keith Cowing
Status Report
November 30, 2023
Filed under , , , , , , ,
JWST/NIRSpec Observations Of The Coldest Known Brown Dwarf
Comparison of spectra for WISE 0855 from Gemini/GNIRS (Skemer et al. 2016; Morley et al. 2018; Miles et al. 2020) and JWST/NIRSpec (this work). — astro-ph.SR

We present 1-5um spectroscopy of the coldest known brown dwarf, WISE J085510.83-071442.5 (WISE 0855), performed with the Near-Infrared Spectrograph (NIRSpec) on board the James Webb Space Telescope (JWST).

NIRSpec has dramatically improved the measurement of spectral energy distribution of WISE 0855 in terms of wavelength coverage, signal-to-noise ratios, and spectral resolution.

We have performed preliminary modeling of the NIRSpec data using the ATMO 2020 models of cloudless atmospheres, arriving at a best fitting model that has T_eff=285 K. That temperature is ~20 K higher than the value derived by combining our luminosity estimate with evolutionary models (i.e., the radius in the model fit to the SED is somewhat smaller than expected from evolutionary models). Through comparisons to the model spectra, we detect absorption in the fundamental band of CO, which is consistent with an earlier detection in a ground-based spectrum and indicates the presence of vertical mixing. Although PH_3 is expected in Y dwarfs that experience vertical mixing, it is not detected in WISE 0855.

Previous ground-based M-band spectroscopy of WISE 0855 has been cited for evidence of H_2O ice clouds, but we find that the NIRSpec data in that wavelength range are matched well by our cloudless model. Thus, clear evidence of H_2O ice clouds in WISE 0855 has not been identified yet, but it may still be present in the NIRSpec data. The physical properties of WISE 0855, including the presence of H_2O clouds, can be better constrained by more detailed fitting with both cloudless and cloudy models and the incorporation of unpublished 5-28um data from the Mid-infrared Instrument on JWST.

K. L. Luhman, P. Tremblin, C. Alves de Oliveira, S. M. Birkmann, I. Baraffe, G. Chabrier, E. Manjavacas, R. J. Parker, J. Valenti

Comments: Astronomical Journal, in press
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2311.17316 [astro-ph.SR] (or arXiv:2311.17316v1 [astro-ph.SR] for this version)
Submission history
From: Kevin Luhman
[v1] Wed, 29 Nov 2023 02:11:17 UTC (542 KB)
Astrobiology, Astrochemistry,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻