Distance Dependence in the Solar Neighborhood Age‐Metallicity Relation

The age-metallicity relation for F and G dwarf stars in the solarneighborhood, based on the stellar metallicity data of Edvardsson et al.(1993), shows an apparent scatter that is larger than expected considering theuncertainties in metallicities and ages. A number of theoretical models havebeen put forward to explain the large scatter. However, we present evidence,based on Edvardsson et al. (1993) data, along with Hipparcos parallaxes and newage estimates, that the scatter in the age-metallicity relation depends on thedistance to the stars in the sample, such that stars within 30 pc of the Sunshow significantly less scatter in [Fe/H]. Stars of intermediate age from theEdvardsson et al. sample at distances 30-80 pc from the Sun are systematicallymore metal-poor than those more nearby. We also find that the slope of theapparent age-metallicity relation is different for stars within 30 pc than forthose stars more distant. These results are most likely an artifact ofselection biases in the Edvardsson et al. star sample. We conclude that theintrinsic dispersion in metallicity at fixed age is < 0.15 dex, consistent withthe < 0.1 dex scatter for Galactic open star clusters and the interstellarmedium.Comment: 15 pages, 5 figures, uses AASTex aaspp4 style; accepted for publication in the Astrophysical Journa