Adopted IMF for chemical evolution of models M4ω4 (solid red line) and M5ω4 (dot-dashed red line). The VMO IMF distributions are given by Eq. (4) with M_char = 200 M_⊙ and normalised to the cumulative mass reached at the corresponding Z_cr. For comparison, the IMFs of the post-VMO burst phases, with the same mass normalisation, are also shown (black lines). The expected number of VMOs is shown in the label and in Table 2.