radiative transfer; methods: numerical; techniques: spectroscopic; planets and satellites: atmospheres; brown dwarfs
Abstract :
[en] Silicate clouds have long been known to significantly impact the spectra of late L-type brown dwarfs ─ with observable absorption features at ~10 μm. The James Webb Space Telescope (JWST) has reopened a window to the mid-infrared with unprecedented sensitivity, bringing the characterization of silicate clouds into focus again. Using JWST, we aim to characterize the planetary-mass brown dwarf PSO J318.5338-22.8603, concentrating on any silicate cloud absorption the object may exhibit. PSO J318's spectrum is extremely red, and its flux is variable, both of which are thought to be hallmarks of cloud absorption. We present JWST NIRSpec PRISM, G395H, and MIRI MRS observations of PSO J318 from 1 to 18 μm. We introduce a method based on PSO J318's brightness temperature to generate a list of cloud species that are likely present in its atmosphere. We tested for the species' presence with petitRADTRANS retrievals. Using retrievals and grids from various climate models, we derived bulk parameters from PSO J318's spectra, which are mutually compatible. Our retrieval results point to a solar to a slightly super-solar atmospheric C/O, a slightly super-solar metallicity, and a <SUP>12</SUP>C/<SUP>13</SUP>C below ISM values. The atmospheric gravity proves difficult to constrain for both retrievals and grid models. Retrievals describing the flux of PSO J318 by mixing two 1D models ("two-column models") appear favored over single-column models; this is consistent with PSO J318's variability. The JWST observations also reveal a pronounced absorption feature at 10 μm. This absorption is best reproduced by introducing a high-altitude cloud layer of small (<0.1 μm) amorphous SiO grains. The retrieved particle size and location of the cloud is consistent with SiO condensing as cloud seeding nuclei. High-altitude clouds comprised of small SiO particles have been suggested in previous studies. Therefore, the SiO nucleation we potentially observe in PSO J318 could be a more widespread phenomenon.
Research Center/Unit :
STAR - Space sciences, Technologies and Astrophysics Research - ULiège
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Mollière, P.; Max-Planck-Institute for Astronomy, Heidelberg
Kühnle, H.; Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang-Pauli-Str 27, 8093, Zürich, Switzerland,
Matthews, E. C.; Max-Planck-Institute for Astronomy, Heidelberg
Henning, Th.; Max-Planck-Institute for Astronomy, Heidelberg
Min, M.; SRON Space Research Organisation Netherlands, Niels Bohrweg 4, 2333, CA, Leiden, The Netherlands,
Patapis, P.; Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang-Pauli-Str 27, 8093, Zürich, Switzerland,
Lagage, P.-O.; CEA Saclay, Service d'Astrophysique
Waters, L. B. F. M.; Radboud University Nijmegen, Department of Astronomy and Physics, -
Güdel, M.; University of Vienna, Department of Astronomy, -
Jäger, C.; Max-Planck-Institute for Astronomy, Heidelberg, University of Jena, Department of Physics and Astronomy
Zhang, Z.; University of California, Santa Cruz, Department of Astronomy and Astrophysics, University of Rochester, Department of Physics and Astronomy
Decin, L.; Katholieke University of Leuven, Astronomical Institute
Biller, B. A.; Royal Observatory Edinburgh, University of Edinburgh, UK
Absil, Olivier ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO)
Argyriou, I.; Katholieke University of Leuven, Astronomical Institute
Barrado, D.; Center for Astrobiology, Madrid
Cossou, C.; Institut de Recherche sur les Lois Fondamentales de l'Universe
Glasse, A.; Royal Observatory Edinburgh
Olofsson, G.; Stockholm University, Department of Astronomy
Pye, J. P.; University of Leicester, Department of Physics and Astronomy
Rouan, D.; LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Sorbonne Paris Cité, CY Cergy Paris Université, CNRS, 5 place Jules Janssen, 92195, Meudon, France
Samland, M.; Max-Planck-Institute for Astronomy, Heidelberg
Scheithauer, S.; Max-Planck-Institute for Astronomy, Heidelberg
Tremblin, P.; CEA Saclay, Service d'Astrophysique, Atomic Energy Commission, Saclay
Whiteford, N.; American Museum of Natural History, New York
van Dishoeck, E. F.; Leiden Observatory
Östlin, G.; Stockholm University, Department of Astronomy
Ray, T.; Dublin Institute for Advanced Studies, School of Cosmic Physics
Calamari, E., Faherty, J. K., Visscher, C., et al. 2024, ApJ, 963, 67
Campos Estrada, B., Lewis, D. A., Helling, C., et al. 2025, A&A, 694, A275
Chabrier, G., Johansen, A., Janson, M., & Rafikov, R. 2014, in Protostars and Planets VI, eds. H. Beuther, R. S. Klessen, C. P. Dullemond, & T. Henning, 619
Charnay, B., Bézard, B., Baudino, J. L., et al. 2018, ApJ, 854, 172
Chen, X., Biller, B. A., Tan, X., et al. 2025, MNRAS, 539, 3758
Chubb, K. L., & Min, M. 2022, A&A, 665, A2
Chubb, K. L., Rocchetto, M., Yurchenko, S. N., et al. 2021, A&A, 646, A21
Coles, P. A., Yurchenko, S. N., & Tennyson, J. 2019, MNRAS, 490, 4638
Cranmer, K., Brehmer, J., & Louppe, G. 2020, PNAS, 117, 30055
Cushing, M. C., Roellig, T. L., Marley, M. S., et al. 2006, ApJ, 648, 614
