Using photo-ionisation models to derive carbon and oxygen gas-phase
  abundances in the rest UV
  We present a new method to derive oxygen and carbon abundances using the
ultraviolet (UV) lines emitted by the gas-phase ionised by massive stars. The
method is based on the comparison of the nebular emission-line ratios with
those predicted by a large grid of photo-ionisation models. Given the large
dispersion in the O/H - C/O plane, our method firstly fixes C/O using ratios of
appropriate emission lines and, in a second step, calculates O/H and the
ionisation parameter from carbon lines in the UV. We find abundances totally
consistent with those provided by the direct method when we apply this method
to a sample of objects with an empirical determination of the electron
temperature using optical emission lines. The proposed methodology appears as a
powerful tool for systematic studies of nebular abundances in star-forming
galaxies at high redshift.
