Metal abundances of field RR Lyraes.

High resolution echelle spectra in the wavelength range 5900-8100A have been analysed to determine Fe, Ca and O abundances of nine bright field RR Lyraes. Firstly we find a systematic difference of 0.10dex between the iron abundance derived from Fe i and Fe ii lines which can be explained by either an error in temperature scale or non-LTE effects. Secondly, using the iron abundance from Fe ii lines (which is less sensitive to either of the above effects) we find a steeper {DELTA}S, [Fe/H] relation than Butler (1975), specifically [Fe/H]=-0.16-0.195{DELTA}S. Thirdly, for the metal-poor RR Lyraes ([Fe/H]<-1) we find [Ca/Fe]=0.41+/-0.20 and [O/Fe]=0.68+/-0.20. The oxygen abundance uses the 7771, 4 and 5 A triplet and includes a non-LTE correction of 0.35 dex based on published non-LTE calculations. The calcium over-abundance is consistent with other halo objects but the oxygen over-abundance is larger, suggesting either an error in the non-LTE calculations or a real difference between RR Lyraes and (the less evolved) halo subdwarfs and giants.