| Abstract: | 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 interstellarmaterial in this disk
was, on average, fairly rich in heavy elements (〈Fe/H]〉 ≈ −0.2) and poorly mixed. However, the metallicity dispersion continuously
decreased with age, from σ
Fe/H] ≈ 0.22 to ≈0.13. All this time, the mean relative abundance of Mg was somewhat higher than the solar value (〈Mg/Fe]〉 ≈ 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. |
