Three methods to identify local Galactic structures

Abstract

Method one: by combining a sampling parameter related to an isolating integral of the stellar motion, an optimisation of the mixture approach, and a maximisation of the partition entropy for the constituent populations of the stellar sample. Method two: by segregating into different kinematical components in terms of the stellar orbital parameters. Method three: by approaching a maximum entropy velocity distribution to samples selected in terms of stellar eccentricity layers. Working samples: HIPPARCOS and Geneva-Copenhagen survey catalog. Results: kinematical characterisation of large-scale structures, such as thin disc, thick disc and halo, and identification of small-scale structures, such as moving groups in the solar neighbourhood. Consequences: confirmation of the Titius--Bode-like law for radial velocity dispersions and explanation of the apparent vertex deviation of the disc from the swinging of two major kinematic groups around the LSR, by predicting a continuously changing orientation of the disc pseudo ellipsoid.