MINDS. Cha Ha 1, A Brown Dwarf With A hydrocarbon-rich Disk

Context. Recent JWST observations have shown that brown dwarfs (BD) are chemically rich, offering valuable insights into giant planet formation.

Aims. As part of the MIRI mid-INfrared Disk Survey (MINDS) JWST guaranteed time program, we aim to characterize the gas and dust composition of the disk around the brown dwarf [NC98] Cha HA 1, hereafter Cha Hα 1, in the mid-infrared.

Methods. We obtain data from the MIRI Medium Resolution Spectrometer (MRS) from 4.9 to 28μm. We use the dust fitting tool DuCK to investigate the dust composition and grain sizes while we identify and fit molecular emission using slab models.

Results. Compared with disks around very low mass stars, clear silicate emission features are seen in this BD disk. In addition, JWST reveals a plethora of hydrocarbons, including C₂H₂, ¹³CCH₂, CH₃, CH₄, C₂H₄, C₄H₂, C₃H₄, C₂H₆, and C₆H₆ which suggest a disk with a gas C/O > 1. Additionally, we detect CO₂, ¹³CO₂, HCN, H₂, and H₂O. CO and OH are absent from the spectrum. The dust is dominated by large ∼4 μm size amorphous silicates (MgSiO₃). We infer a small dust mass fraction (>10%) of 5 μm size crystalline forsterite. We do not detect polycyclic aromatic hydrocarbons.

Conclusions. Cha Hα 1 shows the most diverse chemistry seen to date in a BD protoplanetary disk, consisting of a strong dust feature, 12 carbon-bearing molecules plus H₂, and water. The diverse molecular environment offers a unique opportunity to test our understanding of BD disks chemistry and how it affects the possible planets forming in them.

María Morales-Calderón, Hyerin Jang, Aditya M. Arabhavi, Valentin Christiaens, David Barrado, Inga Kamp, Ewine F. van Dishoeck, Thomas Henning, L. B. F. M. Waters, Milou Temmink, Manuel Güdel, Pierre-Olivier Lagage, Alessio Caratti o Garatti, Adrian M. Glauser, Tom P. Ray, Riccardo Franceschi, Danny Gasman, Sierra L. Grant, Till Kaeufer, Jayatee Kanwar, Giulia Perotti, Matthias Samland, Kamber Schwarz, Marissa Vlasblom, Luis Colina, Göran Östlin

Comments: 16 pages, 14 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2508.05155 [astro-ph.SR] (or arXiv:2508.05155v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2508.05155
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Submission history
From: María Morales-Calderón
[v1] Thu, 7 Aug 2025 08:41:19 UTC (2,282 KB)
https://arxiv.org/abs/2508.05155
Astrobiology, Astrochemistry,