Clouds with a silicate lining: Using JWST spectra to probe atmospheric diversity in young AB Dor L dwarfs

¹ School of Physics, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
² Department of Astrophysics, American Museum of Natural History, Central Park West at 79th St, New York, NY 10024, USA
³ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 1800 Sherman, Evanston, IL 60201, USA
⁴ School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
⁵ Planétarium de Montréal, Espace pour la Vie, 4801 av. Pierre-de Coubertin, Montréal, Québec, Canada
⁶ Trottier Institute for Research on Exoplanets, Université de Montréal, Département de Physique, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7, Canada
⁷ Department of Physics & Astronomy, Amherst College, 25 East Dr., Amherst, MA 01002, USA
⁸ Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
⁹ Centre for Astrophysics Research, Department of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield AL10 9AB, UK
¹⁰ Department of Physics and Astronomy, Hunter College, City University of New York, 695 Park Avenue, New York, NY 10065, USA
¹¹ Department of Astronomy, University of Texas at Austin, 2515 Speedway, Austin, TX 78712, USA
¹² New York University, New York, NY 10003, USA
¹³ Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027, USA
¹⁴ Department of Astronomy & Astrophysics, University of California, Santa Cruz, CA 95064, USA
¹⁵ Department of Physics, Graduate Center, City University of New York, 365 5th Avenue, New York, NY 10016, USA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 5 December 2025
Accepted: 25 March 2026

Abstract

Aims. We present the first full JWST NIRSpec Prism and MIRI LRS 0.6–14 μm (R ~ 100) spectra and analysis of five ~133 Myr L dwarf members of the AB Doradus moving group and one probable ~500 Myr T dwarf of the Oceanus moving group with known inclination angles between ~23–90°: 2MASS J00470038+6803543, 2MASS J03552337+1133437, 2MASS J06420559+4101599, 2MASS J17410280–4642218, 2MASSW J2206450–421721, and 2MASS J22443167+2043433.

Methods. We constructed near-complete spectral energy distributions of each of our objects to measure their bolometric luminosities, and we estimated their fundamental parameters (T_eff, radius, M, and log g). We used cross-sections of relevant gases to identify the species that are present in each atmosphere. Of particular interest is the silicate absorption feature at 8–11 μm, which provides insight into the complex cloud structure of brown dwarfs. We examined this silicate absorption feature in detail and tested whether a latitudinal dependence exists in the silicate absorption feature within a coeval sample of brown dwarfs.

Results. Various molecular absorption bands are visible in our spectra, including H₂O, CH₄, CO, and CO₂. The shape of the silicate absorption feature varies within our sample, and we find that four out of five of our L type objects agree with previously observed trends, namely, that objects viewed equator-on have deeper silicate absorption. We highlight W1741–46 as an outlier in our sample with an unusually strong silicate absorption given its near pole-on orientation. We also present a tentative correlation between the wavelength of peak silicate absorption and inclination, which may suggest variations in cloud chemical composition or physical properties.

Conclusions. We found an unexpected spectral diversity within our sample, which motivates future studies on these objects through atmospheric retrievals, which will determine the silicate cloud composition and reveal whether there exists a trend with inclination.