Oxygen issue in Core Collapse Supernovae

We study the spectroscopic properties of a selected sample of 26 events within Core Collapse Supernovae (CCSNe) family. Special attention is paid to the nebular oxygen forbidden line [O I] 6300,6364\AA\ doublet. We analyze the line flux ratio "$F_{6300}/F_{6364}$", and infer information about the optical depth evolution, densities, volume-filling factors in the oxygen emitting zones. The line luminosity is measured for the sample events and its evolution is discussed on the basis of the bolometric light curve properties in type II and in type Ib-c SNe. The luminosities are then translated into oxygen abundances using two different methods. The resulting oxygen amounts are combined with the recovered $^{56}$Ni masses and compared with theoretical models by means of the "$[O/Fe] .vs. M_{ms}$" diagram. Two distinguishable and continuous populations, corresponding to Ib-c and type II SNe, are found. The higher mass nature of the ejecta in type II objects is also imprinted on the [Ca II] 7291,7324\AA\ over [O I] 6300,6364\AA\ luminosity ratios. Our results may be used as input parameters for theoretical models studying the chemical enrichment of galaxies.