1994A&A...285..440N

The abundance of oxygen in 9 metal-poor stars is derived from high resolution observations of OH lines in the spectral region 3138-3155 A. The same spectra were previously used to determine the beryllium abundance (Gilmore et al. 1992). In addition, Mg, Ca, Ti, Cr, and Fe abundances are derived from accurate equivalent widths of weak atomic absorption lines in the 5100-6100 A spectral region. Atmospheric parameters, T_eff and g, are determined from the Stroemgren photometric indices b-y and c₁. New accurate oscillator strengths for the FeI and FeII lines allow an important check of these parameters as well as the assumption of LTE; the FeI excitation balance is consistent with the photometric temperatures, whereas the FeII/FeI ionization balance suggests an over-ionization of iron amounting to about 0.15 dex with respect to LTE. The derived abundance ratios between the α-elements and Fe are nearly constant in the metallicity range -3.2 ≲[Fe/H]≲-1.8. Any possible scatter of Mg/Fe, Ca/Fe and Ti/Fe in the galactic halo is less than 0.06 dex and an upper limit for the scatter of O/Fe is 0.15 dex. This suggests that the IMF was similar in different regions of the inner halo and that the mixing of nucleosynthesis products was very efficient in galactic regions of typically globular cluster masses.