Solution CMD ofr nearby stars

We present an unprecedentedly detailed view of the evolution of the Milky Way disc at the solar radius. The bulk of star formation started 11-10.5Gyr ago at metallicity around solar, and continued with a slightly decreasing metallicity trend until 6Gyr ago. Between 6 and 4Gyr ago, a notable break in the age-metallicity distribution is observed, with three stellar populations with distinct metallicities (sub-solar, solar, and super-solar), possibly indicating some dramatic event in the life of our Galaxy.

Star formation then resumed 4Gyr ago with a somewhat bursty behaviour, metallicity near solar and average star formation rate higher than in the period before 6Gyr ago. The derived metallicity distribution closely matches precise spectroscopic data, which also show stellar populations deviating from solar metallicity. Interestingly, our results reveal the presence of intermediate-age populations exhibiting both a metallicity typical of the thick disc, approximately [M/H]=~-0.5, and super-solar metallicity.

The many tests performed indicate that, with high-precision photometric and distance data such as that provided by Gaia, CMDft.Gaia is able to achieve a precision of ~10% and an accuracy better than 6% in the dating of stellar populations, even at old ages. A comparison with independent spectroscopic metallicity information shows that metallicity distributions are also determined with high precision, without imposing any a priori metallicity information in the fitting process.

This opens the door to obtaining detailed and robust information on the evolution of the stellar populations of the Milky Way over cosmic time. As an example, we provide in this paper an unprecedentedly detailed view of the age and metallicity distributions of the stars within 100 pc of the Sun.