Homogeneous photometry and metal abundances for a large sample of Hipparcos metal‐poor stars*

Homogeneous photometric data (Johnson V , B‐V , V‐K , Cousins V‐I and Strömgren b‐y ), radial velocities, and abundances of Fe, O, Mg, Si, Ca, Ti, Cr and Ni are presented for 99 stars with high‐precision parallaxes measured by the Hipparcos satellite. These data have been previously used to assist the derivation of accurate distances and ages of Galactic globular clusters. Magnitudes and colours for the programme stars were obtained by combining and standardizing carefully selected literature data available in the Simbad data base, and V and B‐V values measured by the Hipparcos/Tycho mission. Comparison of colours for our targets suggests: (i) ground‐based and Tycho B‐V values agree well for colours bluer than 0.75 mag, but have a lot of scatter for redder colours; (ii) the Hipparcos V‐I colours have a very large scatter and a zero‐point offset of +0.02 mag compared to the literature values. The programme stars have metal abundances in the range −2.5<[Fe/H]<0.2. The spectroscopic observational data set consists of high‐dispersion (15 000< R <60 000), high S/N (>200) spectra obtained at the Asiago and McDonald Observatories for 66 stars. The analysis is carried out following the same precepts as those used in previous papers of this series, and includes corrections for departures from LTE in the formation of the O lines. The main results are: (i) the equilibrium of ionization of Fe is well satisfied in late F‐‐early K dwarfs; (ii) oxygen and α‐elements are overabundant by ∼0.3 dex. This large homogeneous abundance data set has been used to recalibrate the abundance scales of Schuster & Nissen, Ryan & Norris and Carney et al. (1994).