Year: 2026
Type: preprint
Abstract: We present high signal-to-noise, medium resolution (R ~ 1000), time-series JWST/NIRSpec spectra of WISE 0855 (265K), the coldest known brown dwarf. Medium resolution, time-series spectroscopy gives us the power to disentangle the effects of chemistry, temperature, and condensates on this cool world. Our observations span 11 hours with a 15 minute cadence covering 2.87 - 5.27 $μ$m. The strongest time variable spectroscopic feature is carbon monoxide gas absorption producing modulations with a peak-to-peak amplitude up to 10\% at some wavelengths. Using principal component analysis, we show that the variations in carbon monoxide and phosphine correlate with one another. By comparing our data to atmospheric and structure models we present evidence of patchy water clouds within the atmosphere of WISE 0855. We find that variations in CO and PH$_{3}$ abundances must originate from quenched atmospheric pressures while variations in water cloud thickness occurs at lower pressures.
Source: arXiv (Cornell University)
Authors: Miles, Brittany E., Mang, James, Morley, Caroline V., Skemer, Andrew J. I., Rowland, Melanie, Lacy, Brianna, Suarez, Genaro, Visscher, Channon, Apai, Dániel, Bjoraker, Gordon, Carter, Aarynn L., Faherty, Jacqueline K., Fortney, Jonathan J., Fuda, Nguyen, Geballe, Thomas, Kothari, Harshil, Limbach, Mary Anne, Marley, Mark, McCarthy, Allison M., Schneider, Adam, Vos, Johanna, Cushing, Michael, Freedman, Richard, Line, Michael, Lupu, Roxana, Martin, Emily, Wilson, Mikayla J.
Institutions: University of Arizona, The University of Texas at Austin, University of California, Santa Cruz, American Museum of Natural History, Ames Research Center, Space Science Institute, Dordt University, University of Maryland, Baltimore County, Space Telescope Science Institute, NSF NOIRLab, University of Toledo, University of Michigan, Trinity College Dublin, United States Naval Observatory, U.S. Naval Observatory Flagstaff Station, Search for Extraterrestrial Intelligence, Arizona State University, Eureka Scientific
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7213578617