Metal Abundances of one Hundred Hipparcos Dwarfs

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Abundances for Fe, O, and the alpha-elements (Mg, Si, Ca, and Ti) have been derived from high resolution spectra of a sample of about one hundred dwarfs with high precision parallaxes measured by HIPPARCOS. The stars have metal abundances in the range -2.5<[Fe/H]<0.2. The observational data set consists of high dispersion (20,000<R<70,000), high S/N (>200) spectra collected at the Asiago and McDonald Observatories. The abundance analysis followed the same precepts used by Gratton et al. (1997a) for 300 field stars and for giants in 24 globular clusters Carretta and Gratton (1997), and includes corrections for departures from LTE in the formation of O lines. Our main results are: 1. the equilibrium of ionization of Fe is well satisfied in late F -- early K dwarfs 2. O and alpha-elements are overabundant by 0.3dex This large homogeneous data set was used in the derivation of accurate ages for globular clusters.