  The debate on the oxygen abundances of metal-poor stars has its origin in
contradictory results obtained using different abundance indicators. To achieve
a better understanding of the problem we have acquired high quality spectra
with the Ultraviolet and Visual Echelle Spectrograph at VLT, with a
signal-to-noise of the order of 100 in the near ultraviolet and 500 in the
optical and near infrared wavelength range. Three different oxygen abundance
indicators, OH ultraviolet lines around 310.0 nm, the [OI] line at 630.03 nm
and the OI lines at 777.1-5 nm were observed in the spectra of 13 metal-poor
subgiants with -3.0<=[Fe/H]<=-1.5. Oxygen abundances were obtained from the
analysis of these indicators which was carried out assuming local thermodynamic
equilibrium and plane-parallel model atmospheres. Abundances derived from OI
were corrected for departures from local thermodynamic equilibrium. Stellar
parameters were computed using Teff-vs-color calibrations based on the infrared
flux method and Balmer line profiles, Hipparcos parallaxes and FeII lines.
[O/Fe] values derived from the forbidden line at 630.03 nm are consistent with
an oxygen/iron ratio that varies linearly with [Fe/H] as
[O/Fe]}=-0.09(+/-0.08)[Fe/H]+0.36(+/-0.15). Values based on the OI triplet are
on average 0.19+/-0.22 dex(s.d.) higher than the values based on the forbidden
line while the agreement between OH ultraviolet lines and the forbidden line is
much better with a mean difference of the order of -0.09+/-0.25 dex(s.d.). In
general, our results follow the same trend as previously published results with
the exception of the ones based on OH ultraviolet lines. In that case our
results lie below the values which gave rise to the oxygen abundance debate for
metal-poor stars.
