Analysis of the velocity field of F and G dwarfs in the solar neighborhood as a function of age

The space velocities from the catalog of Nordstrom et al. (2004) are used to trace variations of a number of kinematic parameters of single F and G dwarfs as a function of their age. The vertex deviation of disk stars increases from 7 degrees +/- 1 degrees to 15 degrees +/- 2 degrees as the mean age decreases from 4.3 to 1.5 Gyr. The two-dimensional velocity distributions in the UV, UW, and VW planes are analyzed. The evolution of the main peaks in the velocity distributions can be followed to an average age of approximate to 9 Gyr. We find that: (1) in the distributions of the UV velocity components, stars of different types are concentrated toward several stable peaks (the Hyades, Pleiades, and Sirius Cluster), suggesting that the stars belonging to these formations did not form simultaneously; (2) the peak associated with the Hyades Cluster dominates in all age intervals; and (3) the Hyades peak is strongest for stars with an average age of 1.5 Gyr, suggesting that this peak contains a considerable fraction of stars from the Hyades cluster. The age dependences of the kinematic parameters exhibit a break near approximate to 4-5 Gyr, which can be explained as an effect of the different contributions of stars of the thin and thick disks. The Stromberg relation yields a solar LSR velocity of V-circle dot LSR = (8.7, 6.2, 7.2) +/- (0.5, 2.2, 0.8) km/s.