ON THE BIRTH-PLACE OF THE SUN AND THE PLACES OF FORMATION OF OTHER NEARBY STARS

The Sun has a [Fe/H] metallicity which is larger by +0.17 +/- 0.04 dex than the average metallicity of nearby stars of solar age. This resul t is derived from an age-metallicity relation based on the very accura te data published by Edvardsson et al. (1993) for nearby F and G dwarf s. We adopt a radial galactic gradient in metallicity of partial deriv ative[Fe/H]/partial derivative R = -0.09 +/- 0.02 dex/kpc, independent of the age of the stars. From the solar anomaly and this galactic gra dient, we derive that the Sun has been formed at a galactocentric dist ance R(i,.) = 6.6 +/- 0.9 kpc, if we adopt R(0) = 8.5 kpc for the pres ent distance of the Sun from the galactic center. Hence the Sun has mi grated from its birth-place in the inner part of the Galaxy outwards b y 1.9 +/- 0.9 kpc during its lifetime of 4.5 . 10(9) years. This amoun t is in good agreement with predictions on the diffusion of stellar or bits in space which are based on the observed relation between velocit y dispersion and age of nearby stars (i.e. on the diffusion in velocit y space). The accurate determination of metallicities, coupled with a galactic gradient in metallicity, allows us to investigate empirically the diffusion of stellar orbits in space, at least in galactocentric distance. A direct consequence of this diffusion, and hence a good con firmation of it, is the increase in the dispersion of metallicities of nearby stars with increasing age. From such a relation, we derive als o that the initial dispersion of metallicities is rather small. This i s favourable for deriving the birth-place of the Sun from its anomaly in metallicity.