Summary of our main results. Same as Fig. 12, but with HR 8799e and HR 8799d. Top panel: 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 (represented by the blue stars). The carbon and oxygen abundances of the stars are shown with the dashed lines (HD 4747) and dashed dot lines (HR 8799). Bottom panel: companion elemental abundances normalized to its stellar values with the dashed black line denoting parity.