Retrieved transmission spectra, P-T profile, C/O, and metallicity posteriors of HD 209458 b with equilibrium chemistry. The top panel consists of median transmission spectra and P-T profile of HD 209458 b for the three retrievals, JWST (NIRCam), WFC3 + NIRCam, and STIS + WFC3 + NIRCam. All the spectra shown here are generated with 5000 random equal-weighted samples from PyMultiNest and binned at a resolution of R ∼ 200. The shaded region indicates the 1σ uncertainty in the median fit. JWST observations are represented in green, while combined STIS and WFC3 observations are shown in brown. A retrieved median offset of 39 ppm is applied to the STIS + WFC3 observations, whereas the offset for WFC3 in the case of the WFC3 + JWST combination is not shown here. For all the retrievals, the corresponding P-T profiles are shown beside the median spectra. The bottom panel shows the posteriors of C/O and ﹩{\mathrm{log}}\,(Z)﹩ by varying C and varying O for the C/O ratio. The posterior values shown in this panel correspond to the results shown in Table 5.