Stellar populations of a local sample from its velocity distribution

Extract

In the solar neighbourhood, we can assume that a stellar sample is composed of two stellar populations: thin disk and thick disk stars. If we assume as the only hypothesis that each stellar component is associated with a Schwarzchild velocity distribution function (e.g., Sanz, J., Juan, J.M., this symposium), then it is possible to determine the velocity distribution of both components (Cubarsi, R.: 1990, AJ 99, 1558). Thus, starting from the central velocity moments up to fourth order of the overall stellar sample we obtain the partial moments, the difference between centroid velocities and the percentage of mixture. Moreover, a set of 25 constraint equations between the total moments is determined. This method has been applied to some local stellar samples under the hypothesis of a two-component mixture (Hernandez-Pajares, M.: 1991, this symposium) and the obtained kinematical features of the stellar components are in agreement with kinematical properties of thin disk and thick disk stars described from other physical viewpoints (e.g., Sandage, A.: 1987, in The Galaxy, eds. G. Gilmore, R.F. Carswell (Reidel), p. 321).