The distinct formation pathways proposed for directly imaged exoplanets and isolated brown dwarfs might leave imprints in the inherited chemical composition. Elemental and isotopic tracers could help inform the suspected histories, but this requires a careful characterisation of the sub-stellar atmospheres. In particular, objects at the L-T transition exhibit signs of dynamics that can drive their atmospheres out of chemical equilibrium. In this work, we studied the nearest L-T brown dwarfs, Luhman 16A and B, to assess the chemical disequilibrium in their atmospheres. We also investigated the elemental and isotopic compositions in the context of their probable formation history within the Oceanus moving group. As part of the ESO SupJup Survey, we obtained spatially resolved CRIRES+ K-band spectra of the binary. These high-resolution observations were analysed using an atmospheric retrieval framework that couples the radiative transfer code to the sampling algorithm. petitRADTRANS MultiNest We detect and retrieve the abundances of 12 CO, H₂O, CH₄, NH₃, H₂S, HF, and the ¹3CO isotopologue. We find that both atmospheres are in chemical disequilibrium with somewhat stronger vertical mixing in Luhman 16A compared to B (K_ ∼, 10⁸. 7 vs K_ zz, A zz, B 8. 2 cm² -1). The tested chemical models, free-equilibrium and disequilibrium chemistry, yield consistent mixing ratios and agree with earlier work at shorter wavelengths. The free-chemistry gaseous ∼, 0. 15. The carbon isotope ratios are measured at mathrm ratios show evidence of oxygen trapping in silicate-oxide clouds. While the ratios are consistent with the solar composition, the metallicities are modestly enhanced with mathrm C/H ^ 12 C/^ 13 CA =74^ +2 _ -2 and =74^ ^ 12 C/^ 13 CB +3 _ -3. The coincident constraints of metallicities and isotopes across the binary provide further evidence in favour of a common formation. The mathrm ^ 12 C/^ 13 C ratios are aligned with the present-day interstellar medium but lower than the Solar System value. This suggests a recent inheritance and corroborates the relatively young age (∼, 500 Myr) of Luhman 16A and B as members of the Oceanus moving group.
Regt et al. (Wed,) studied this question.