HST trigonometric distances , photometric metallicities , isochronic ages from the second revised version of the Geneva–Copenhagen survey , and uniform spectroscopic Fe and Mg abundances from our master catalog are used to construct and analyze the age–metallicity and age–relative Mg abundance relations for stars of the thin disk .
The influences of selection effects are discussed in detail .
It is demonstrated that the radial migration of stars does not lead to appreciable distortions in the age dependence of the metallicity .
During the first several billion years of the formation of the thin disk , the interstellar material in this disk was , on average , fairly rich in heavy elements ( \langle [ Fe / H ] \rangle \approx - 0.2 ) and poorly mixed .
However , the metallicity dispersion continuously decreased with age , from \sigma _ { [ Fe / H ] } \approx 0.22 to \approx 0.13 .
All this time , the mean relative abundance of Mg was somewhat higher than the solar value ( \langle [ Mg / Fe ] \rangle \approx 0.1 ) .
Roughly four to five billion years ago , the mean metallicity began to systematically increase , while retaining the same dispersion ; the mean relative Mg abundance began to decrease immediately following this .
The number of stars in this subsystem increased sharply at the same time .
These properties suggest that the star-formation rate was low in the initial stage of formation of the thin disk , but abruptly increased about four to five billion years ago . Keywords : age–metallicity relation , thin disk of the Galaxy