CENTRAL MOMENTS OF THE VELOCITY DISTRIBUTION FROM A SUPERPOSITION OF 2 STELLAR-SYSTEMS

From an analytical viewpoint, the superposition of two stellar velocity distribution functions and the set of central velocity moments up to fourth order are studied. For the Galaxy, any specific type of symmetry or differential movement has not been assumed. General expressions of the total central moments starting from the partial ones, which are associated with both distribution function components, are obtained and, when each component is quadratic in peculiar velocities and of Schwarzschild type, the constraints between the total central moments are studied. Moreover, a general method to calculate the partial velocity distributions and population percentage working from the total central moments of a two-component stellar sample is described. In order to characterize in a kinematical way the stellar populations in the solar neighborhood, the method is applied to some local stellar samples.