[O/Fe] versus [Fe/H] of MW disc and halo dwarf stars from Amarsi et al. (2019). Blue points indicate stars which were used to estimate the [O/Fe]_CCSN shown in Figure 6. Their average < [O/Fe]_MW >  = 0.52 dex is indicated by the thick black line. Thin grey lines span between 13 and 99.8 percentiles of the average ([O/Fe] = 0.48-0.56 dex). Amarsi et al. (2019) measure relative abundances with respect to the Sun and derive log₁₀(O/Fe)_⊙ = 1.179 dex. For consistency with the rest of the analysis, we convert those relative measurements to absolute abundances and place them on GS98 solar scale. The thin dashed lines show the solar values from Amarsi et al. (2019).