CHEMICAL EVOLUTION OF THE GALACTIC DISK - EVIDENCE FOR A GRADIENT PERPENDICULAR TO THE GALACTIC PLANE

An improved DDO abundance calibration presented in a previous paper is used to derive overall [Fe/H] abundances for 233 red giants in a samp le of 63 open clusters with a wide range of ages. Membership of the gi ants in each cluster is confirmed by using velocity, astrometric, and photometric information. the newly derived abundances allow us: (1) to confirm the absence of a global age-metallicity relation for the enti re open cluster sample; (2) to define a homogeneous abundance scale fo r the Galactic open cluster system. If this scale is adopted, a radial abundance gradient (o[Fe/H]/partial derivative R(gc) = -0.07 dex kpc( -1)) as well as a steeper abundance gradient perpendicular to the Gala ctic plane (partial derivative[Fe/H]/partial derivative\Z\ = -0.34 dex kpc(-1)) are found. Orbital motions for a subsample of 19 open cluste rs with sufficiently good distances and kinematical data are calculate d by assuming a Miyamoto-type gravitational potential for the Galaxy. The dynamical evolution of each cluster is computed backwards for a ti me interval equal to its age and some relevant parameters of each clus ter orbit are derived. It is found that both the radial and Z gradient s determined from the observed cluster positions are very close to the paleogradient ones, namely, the gradients in metallicity of the gas o ut of which the clusters have been generated. (C) 1995 American Astron omical Society.