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 Stromgre n 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 th e Hipparcos satellite. These data have been previously used to assist the d erivation of accurate distances and ages of Galactic globular clusters. Mag nitudes and colours for the programme stars were obtained by combining and standardizing carefully selected literature data available in the Simbad da ta base, and V and B-V values measured by the Hipparcos/Tycho mission. Comp arison 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 scatte r for redder colours; (ii) the Hipparcos V-l colours have a very large scat ter 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. T he spectroscopic observational data set consists of high-dispersion (15 000 < R < 60 000), high S/N (> 200) spectra obtained at the Asiago and McDonal d Observatories for 66 stars. The analysis is carried out following the sam e precepts as those used in previous papers of this series, and includes co rrections 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 oc-elements are overabundant by simi lar to 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.