Year: 2025
Type: article
Abstract: Context. With a temperature of ∼285 K, WISEJ0855–0714 (hereafter, WISE 0855) is the coldest brown dwarf observed thus far. Studying such cold gas giants allows us to probe the atmospheric physics and chemistry of evolved objects that resemble Solar System gas giants. Aims. Using James Webb Space Telescope (JWST), we obtained observations to characterize WISE 0855’s atmosphere, focusing on vertical variation in the water steam abundance, measuring trace gas abundances, and obtaining the bulk parameters for this cold object. Methods. We observed the ultra-cool dwarf WISE 0855 using the Mid-Infrared Instrument Medium Resolution Spectrometer (MIRI/MRS) on board JWST at a spectral resolution of up to 3750. We combined the observation with published data from the Near-Infrared Spectrograph (NIRSpec) G395M and PRISM modes, yielding a spectrum ranging from 0.8 to 22 µm. We applied atmospheric retrievals using petitRADTRANS to measure the atmospheric abundances, pressure-temperature structure, radius, and gravity of the brown dwarf. We also employed publicly available clear and cloudy self-consistent grid models to estimate the bulk properties of the atmosphere such as the effective temperature, radius, gravity, and metallicity. Results. Atmospheric retrievals have constrained a variable water abundance profile in the atmosphere, as predicted by equilibrium chemistry. We detected the 15NH3 isotopolog and inferred a ratio of volume fraction of 14NH3/15 NH3 = 349−41+53 for the clear retrieval. We measured the bolometric luminosity by integrating the presented spectrum, obtaining a value of log(L/L⊙) = −7.291 ± 0.008. Conclusions. The detected water depletion indicates that water condenses out in the upper atmosphere due to the very low effective temperature of WISE 0855. The height in the atmosphere where this occurs is covered by the MIRI/MRS data, thereby demonstrating the potential of MIRI to characterize the atmospheres of cold gas giants. After comparing the data to retrievals and self-consistent grid models, we did not detect any signs of water ice clouds, although their spectral features have been predicted in previous studies.
Authors: H. Kühnle, P. Patapis, P. Mollière, P. Tremblin, E. Matthews, A. M. Glauser, N. Whiteford, M. Vasist, O. Absil, D. Barrado, M. Min, P.-O. Lagage, L. B. F. M. Waters, M. Guedel, Th. Henning, B. Vandenbussche, P. Baudoz, L. Decin, J. P. Pye, P. Royer, E. F. van Dishoeck, G. Östlin, T. P. Ray, G. Wright
Institutions: ETH Zurich, Institute for Particle Physics and Astrophysics, Max Planck Institute for Astronomy, Centre National de la Recherche Scientifique, Université de Versailles Saint-Quentin-en-Yvelines, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay, Maison de la Simulation, CEA Paris-Saclay, American Museum of Natural History, University of Liège, Centro de Astrobiología, Space Research Organisation Netherlands, Université Paris Cité, Astrophysique, Instrumentation et Modélisation, Radboud University Nijmegen, KU Leuven, Université Paris Sciences et Lettres, Observatoire de Paris, Sorbonne Université, Laboratoire d’études spatiales et d’instrumentation en astrophysique, University of Leicester, Leiden University, Leiden Observatory, Stockholm University, Dublin Institute For Advanced Studies, Royal Observatory, UK Astronomy Technology Centre
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, National Aeronautics and Space Administration, European Space Agency, European Commission, National Research Foundation, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Danmarks Grundforskningsfond, Swedish National Space Agency, Fonds De La Recherche Scientifique - FNRS, Belgian Federal Science Policy Office, Centre National d’Etudes Spatiales, Fonds Wetenschappelijk Onderzoek, KU Leuven, Max-Planck-Institut für Astronomie, Horizon 2020 Framework Programme, Science and Technology Facilities Council, Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture, Agencia Estatal de Investigación
Awards: G1276317268, Collaborative Research: Using Brown Dwarfs to Understand Exoplanetary Atmospheres: Spectral Inversions of an Analog Population, G1727239079, G2001806450, G2188020438, G2350454921, Virtual Laboratories for Exoplanets and Planet Forming Disks, G3345895242, G3401686495, G3480869486, CAREER: Understanding Our Dynamic, Young, Solar Neighborhood, G4367447019, G4484233699, Characterisation of the effect of stellar variability on exoplanet signatures, G5080475149, G5145896149, G5175525644, G5392910068, G5972664074, G6281504974, G6336900812, G6638315758, G6687328476, G6890900265, G7084143925, Constraining gas giant planet formation via high-contrast exoplanet imaging, G7628805400, G7984235579, G8512683158, G8684520763
OpenAlex ID: W6903281470
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