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 sample of 63 open clusters with a wide range of ages. Membership of the giants 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 entire open cluster sample; (2) to define a homogeneous abundance scale for 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 Galactic plane (partial derivative[Fe/H]/partial derivative\Z\ = -0.34 dex kpc(-1)) are found. Orbital motions for a subsample of 19 open clusters with sufficiently good distances and kinematical data are calculated by assuming a Miyamoto-type gravitational potential for the Galaxy. The dynamical evolution of each cluster is computed backwards for a time interval equal to its age and some relevant parameters of each cluster orbit are derived. It is found that both the radial and Z gradients determined from the observed cluster positions are very close to the paleogradient ones, namely, the gradients in metallicity of the gas out of which the clusters have been generated. (C) 1995 American Astronomical Society.