Oxygen-to-iron ratios in the Galactic metal-poor stars (following Fig. 4 from Dobrovolskas et al. 2015). Solid grey circles depict [O/Fe] ratios in red giants, subgiants, and main sequence stars determined using the forbidden [O i] 630 nm line (literature data; see Dobrovolskas et al. 2015, for details). Red triangles show 3D LTE and 1D LTE [O/Fe] ratios in four metal-poor giants obtained from OH IR lines by Dobrovolskas et al. (2015, open and filled symbols, respectively). The [O/Fe] ratios determined in these stars from [O i] line are indicated as black solid circles. Blue triangles are average [O/Fe] ratios in HD 122563 obtained in this study from 71 OH UV lines (for readability, abundances determined from OH UV and IR lines are shifted horizontally by ±0.03 dex). The solid line is the evolutionary model of François et al. (2004). Note that all abundance ratios are given in the reference scale, where the solar oxygen abundance is A(O) = 8.76 (Steffen et al. 2015).