Physical origin of deep iron opacity

Determine the detailed physical origin of the compact, deep iron opacity source retrieved near pressures of several bars in the atmospheres of HD 89744B, GJ 1048B, and LSPM J0632+5053B, including whether it is produced by iron particles surviving into hotter undersaturated layers or by additional unmodeled deep, nearly gray opacity.

Background

The physical-cloud retrievals identify compact Fe opacity at approximately 3–4 bar in all three benchmark early-L dwarfs, even though the equilibrium Fe condensation boundaries occur at substantially lower pressures. The paper discusses finite evaporation regions as one possible explanation: settling iron particles may persist into hotter, undersaturated layers while gradually evaporating. However, the retrieved Fe component could alternatively represent another deep, nearly gray opacity source that is not included in the adopted condensate set. The observations therefore establish the presence of deep opacity but do not uniquely identify its physical origin.

References

The retrieved Fe component may also represent additional deep, nearly gray opacity that is not explicitly included in the adopted condensate set. The present spectra therefore support a compact deep opacity source, while its detailed physical origin remains uncertain.

— Gaseous SiO and Silicate Clouds in Three Benchmark Early-L Dwarfs  (2610.11530 - Tu et al., 8 Oct 2026) in Section 4.5, subsection “Deep Fe Cloud Structure”