Keck NIRSPEC Infrared OH Lines: Oxygen Abundances in Metal‐poor Stars down to [Fe/H] = −2.9

Infrared OH lines at 1.5-1.7 μm in the H band were obtained with the NIRSPEC high-resolution spectrograph at the 10 m Keck Telescope for a sample of seven metal-poor stars. Detailed analyses have been carried out, based on optical high-resolution data obtained with the Fiber-fed Extended Range Optical Spectrograph at ESO. Stellar parameters were derived by adopting infrared flux method effective temperatures, trigonometric and/or evolutionary gravities, and metallicities from Fe II lines. We obtain that the sample stars with metallicities [Fe/H] < -2.2 show a mean oxygen abundance [O/Fe] ≈ 0.54 for a solar oxygen abundance of (O) = 8.87, or [O/Fe] ≈ 0.64 if (O) = 8.77 is assumed.