Oxygen abundances of halo dwarf and subgiant stars from VLT/UVES observations of the [OI] lambda 6300 line

The forbidden oxygen line at 6300 Angstrom has been observed with UVES on t he ESO VLT for 13 dwarf and subgiant stars ranging in metallicity from [Fe/ H]similar or equal to -0.7 to - 1.8. The spectra obtained have a resolution of R = 55 000 and SIN similar or equal to 400. After removal of telluric l ines, the equivalent width of the [O (I)] line could be measured with an ac curacy of 0.2 to 0.3 M Angstrom. Using these data and the equivalent widths of eight weak Fe (II) lines, the trend of [O/Fe] with [Fe/H] has been deri ved. Below [Fe/H]similar or equal to - 1.0 the oxygen-to-iron ratio is near ly constant at a level of [O/Fe] similar or equal to 0.4 in contradiction t o recent results from UV OH lines. (C) 2001 Elsevier Science B.V. All right s reserved.