Amortized Opacity Marginalization Improves C/O Interval Calibration for Brown-Dwarf Retrievals
I train neural posterior estimators to account for uncertain molecular opacities in brown-dwarf spectra. On perturbed simulated spectra, opacity marginalization improves nominal 90% C/O interval coverage from 61.4% to 89.4% in matched three-seed ensembles. On JWST spectra of 14 brown dwarfs, the final ensemble contains the published C/O of a T8 benchmark that every fixed-opacity network misses.