Carbon and oxygen in HII regions of the Magellanic Clouds: abundance
  discrepancy and chemical evolution
  We present C and O abundances in the Magellanic Clouds derived from deep
spectra of HII regions. The data have been taken with the Ultraviolet-Visual
Echelle Spectrograph at the 8.2-m VLT. The sample comprises 5 HII regions in
the Large Magellanic Cloud (LMC) and 4 in the Small Magellanic Cloud (SMC). We
measure pure recombination lines (RLs) of CII and OII in all the objects,
permitting to derive the abundance discrepancy factors (ADFs) for O^2+, as well
as their O/H, C/H and C/O ratios. We compare the ADFs with those of other HII
regions in different galaxies. The results suggest a possible metallicity
dependence of the ADF for the low-metallicity objects, but more uncertain for
high-metallicity objects. We compare nebular and B-type stellar abundances and
we find that the stellar abundances agree better with the nebular ones derived
from collisionally excited lines (CELs). Comparing these results with other
galaxies we observe that stellar abundances seem to agree better with the
nebular ones derived from CELs in low-metallicity environments and from RLs in
high-metallicity environments. The C/H, O/H and C/O ratios show almost flat
radial gradients, in contrast with the spiral galaxies where such gradients are
negative. We explore the chemical evolution analysing C/O vs. O/H and comparing
with the results of HII regions in other galaxies. The LMC seems to show a
similar chemical evolution to the external zones of small spiral galaxies and
the SMC behaves as a typical star-forming dwarf galaxy.
