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.
