Radial oxygen abundance distribution in NGC 5457. Panel a: calibration-based oxygen abundances for the compilation of the slit spectra of H II regions. The grey circles denote the (O/H)_R abundances for individual measurements and the black solid line is the best linear fit to those data. The green plus symbols are the (O/H)_S abundances for individual measurements and the dashed line is the best linear fit to those data. Panel b:T_e-based oxygen abundances with measured electron temperatures t_2, N (circles) and t_3,O (plus signs) in H II regions from Croxall et al. (2016). The solid line is the (O/H)_R–R relation from panel (a). Panel c: same as panel (b) but for the sample of H II regions from Esteban & Bresolin (2020).