[X/H] versus . Stars and circles represent ONC and OB1b targets, respectively. Mean ONC and OB1b values and  ± 1σ bars are shown as dashed areas, 45° and 215° oriented, respectively. For the Na, Al, Ca, and Ti abundances, we show the mean values obtained from all the ONC targets with K, while for the Si, Ni, and mean Ti abundances the average was computed considering all the ONC/OB1b stars. The horizontal error bar in all plots represents the typical uncertainty in .