Distance dependence in the solar neighborhood age-metallicity relation

The age-metallicity relation for F and G dwarf stars in the solar neighborh ood, based on the stellar metallicity data of Edvardsson et al., shows an a pparent scatter that is larger than expected considering the uncertainties in metallicities and ages. A number of theoretical models have been put for ward to explain the large scatter. However, we present evidence, based on t he Edvardsson et al. data, along with Hipparcos parallaxes and new age esti mates, that the scatter in the age-metallicity relation depends on the dist ance to the stars in the sample, such that stars within 30 pc of the Sun sh ow significantly less scatter in [Fe/H]. Stars of intermediate age from the Edvardsson et al. sample at distances 30-80 pc from the Sun are systematic ally more metal poor than those more nearby. We also find that the slope of the apparent age-metallicity relation is different for stars within 30 pc than for those stars more distant. These results are most likely an artifac t of selection biases in the Edvardsson ct al. star sample. We conclude tha t the intrinsic dispersion in metallicity at fixed age is less than 0.15 de x for field stars in the solar neighborhood, consistent with the less than 0.1 dex for Galactic open star clusters and the interstellar medium.