Results from the atmospheric retrieval analysis. Top panel: the retrieved water mixing ratios and elemental abundances of carbon and oxygen for HD 4747B, and for the four HR 8799 exoplanets as a function of the distance to the host star. For HR 8799d and e, we show the water abundance in chemical equilibrium at 1 bar (blue stars). The carbon abundance retrieved for these two planets is very low and is not shown (see Fig C.4). The carbon and oxygen abundances of the stars are shown with the dashed lines (HD 4747) and dash-dotted lines (HR 8799). Bottom panel: the companion elemental abundances normalized to its stellar values with the dashed black line denoting parity.