We use proper motions and parallaxes from the new reduction of Hipparcos data and Geneva-Copenhagen radial velocities for a complete sample of \sim 15 000 main-sequence and subgiant stars , and new Padova isochrones to constrain the kinematics and star-formation history of the solar neighbourhood .
We rederive the solar motion and the structure of the local velocity ellipsoids .
When the principal velocity dispersions are assumed to increase with time as t ^ { \beta } , the index \beta is larger for \sigma _ { W } ( \beta _ { W } \approx 0.45 ) than for \sigma _ { U } ( \beta _ { U } \approx 0.31 ) .
For the three-dimensional velocity dispersion we obtain \beta = 0.35 .
We exclude saturation of disc heating after \sim 3 { Gyr } as proposed by Quillen & Garnett ( 44 ) .
Saturation after \ga 4 { Gyr } combined with an abrupt increase in velocity dispersion for the oldest stars can not be excluded .
For all our models the star-formation rate is declining , being a factor 2–7 lower now than it was at the beginning .
Models in which the SFR declines exponentially favour very high disc ages between 11.5 and 13 { Gyr } and exclude ages below \sim 10.5 { Gyr } as they yield worse fits to the number density and velocity dispersion of red stars .
Models in which the SFR is the sum of two declining exponentials representing the thin and thick discs favour ages between 10.5 and 12 { Gyr } with a lower limit of \sim 10.0 { Gyr } .
Although in our models the star-formation rate peaked surprisingly early , the mean formation time of solar-neighbourhood stars is later than in ab-initio models of galaxy formation , probably on account of weaknesses in such models .