Temperature, MMW, and VMR as a function of pressure for the chemical equilibrium model of WASP-189 b. The P-T profile comes from F. Yan et al. (2020). The MMW and VMR values have been computed from the P-T profile using the FASTCHEM chemical equilibrium solver, assuming solar elemental abundances. For visual purposes we plot a selection of those most relevant to this work, although chemical abundances of additional atmospheric species were computed with FASTCHEM and included in the MMW. Left panel: P-T and MMW profiles. Middle panel: VMRs for the species shown in the legend below. The chemical profiles most relevant to this work (Fe, Si, Cr, Al) have been highlighted using thicker lines. Right panel: the emission contribution function for the fiducial spectral template. A spectral line core of neutral iron is highlighted, which forms at pressures of ∼0.1–1 mbar.