The local star formation history of the thin disc derived from kinematic data

Context. We present an evolutionary disc model for the thin disc in the solar cylinder based on a continuous star formation history (SFR) and a continuous dynamical heating (AVR) of the stellar subpopulations. Aims. We determine the star formation history of the thin disc in the solar vicinity. The self-consistent model of the vertical structure allows predictions of the density, age, metallicity and velocity distribution of main sequence stars as a function of height above the midplane. Methods. The vertical distribution of the stellar subpopulations are calculated self-consistently in dynamical equilibrium. The SFR and AVR of the stellar subpopulations are determined by fitting the velocity distribution functions of main sequence stars. Results. We find a vertical disc model for the thin disc including the gas and dark matter component, which is consistent with the local kinematics of main sequence stars and fulfils the known constraints on the surface densities and mass ratios. The SFR shows a maximum 10 Gyr ago declining by a factor of 10 until present time. The velocity dispersion of the stellar subpopulations increase with age according to a power law with index 0.375. Using the new scale heights leads to a best fit IMF with power-law indices of 1.5 below and 4.0 above 1.6M⊙, which has no kink around 1M⊙. Including a thick disc component results in slight variations of the thin disc properties, but has a negligible influence on the SFR. A variety of predictions are made concerning the number density, age and metallicity distributions of stellar subpopulations as a function of z above the galactic plane. Conclusions. The combination of kinematic data from Hipparcos and the finite lifetimes of main sequence stars allows strong constraints on the structure and history of the local disc. A constant SFR can be ruled out.