Gaseous SiO and Silicate Clouds in Three Benchmark Early-L Dwarfs
Abstract
Tracing silicon from gaseous SiO into silicate condensates provides a direct view of the condensation process that forms silicate clouds in L-dwarf atmospheres. Here we present evidence for gaseous SiO in three benchmark early-L dwarfs, HD 89744B, GJ 1048B, and LSPM J0632+5053B, using JWST/NIRSpec and MIRI spectroscopy. Atmospheric retrievals with and without SiO under multiple cloud prescriptions identify the strongest SiO signatures at 4.0--4.2 and 7.7--8.2 μm, with the local likelihood diagnostic reaching 4.6σ. In the physical cloud retrievals, the 8 μm band probes lower pressures than the 4 μm overtone, reaching atmospheric layers where equilibrium SiO is more strongly depleted by silicate condensation. All three objects also show compact Fe opacity at pressures of a few bar. Their inferred gas-phase C/O ratios are consistent with expectations from the host-star compositions after accounting for refractory oxygen sequestration. Within the adopted Mie treatment of amorphous silicate grains, the silicate mineralogies favor Mg2SiO4 for HD 89744B and a mixed Mg2SiO4+MgSiO3 cloud for GJ 1048B. Extending this framework to cooler L dwarfs will trace the coupled evolution of gaseous SiO depletion and silicate-cloud formation along the L-dwarf sequence.
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BibTeX
@misc{tu2026gaseous,
title = {{Gaseous SiO and Silicate Clouds in Three Benchmark Early-L Dwarfs}},
author = {Zhijun Tu and Shu Wang and Xiaodian Chen and Haomiao Huang and Jifeng Liu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.11530},
eprint = {2610.11530},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.11530},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Gaseous SiO and Silicate Clouds in Three Benchmark Early-L Dwarfs
AU - Zhijun Tu
AU - Shu Wang
AU - Xiaodian Chen
AU - Haomiao Huang
AU - Jifeng Liu
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2610.11530
UR - https://arxiv.org/abs/2610.11530
AB - Tracing silicon from gaseous SiO into silicate condensates provides a direct view of the condensation process that forms silicate clouds in L-dwarf atmospheres. Here we present evidence for gaseous SiO in three benchmark early-L dwarfs, HD 89744B, GJ 1048B, and LSPM J0632+5053B, using JWST/NIRSpec and MIRI spectroscopy. Atmospheric retrievals with and without SiO under multiple cloud prescriptions identify the strongest SiO signatures at 4.0--4.2 and 7.7--8.2 μm, with the local likelihood diagnostic reaching 4.6σ. In the physical cloud retrievals, the 8 μm band probes lower pressures than the 4 μm overtone, reaching atmospheric layers where equilibrium SiO is more strongly depleted by silicate condensation. All three objects also show compact Fe opacity at pressures of a few bar. Their inferred gas-phase C/O ratios are consistent with expectations from the host-star compositions after accounting for refractory oxygen sequestration. Within the adopted Mie treatment of amorphous silicate grains, the silicate mineralogies favor Mg_2SiO_4 for HD 89744B and a mixed Mg_2SiO_4+MgSiO_3 cloud for GJ 1048B. Extending this framework to cooler L dwarfs will trace the coupled evolution of gaseous SiO depletion and silicate-cloud formation along the L-dwarf sequence.
ER -