Discontinuities of the local velocity distribution which are associated with stellar populations
are studied from the improved statistical method MEMPHIS (Maximum Entropy of
the Mixture Probability from HIerarchical Segregation), by combining a sampling parameter,
optimisation of the mixture approach, and maximum partition entropy of populations
composing the stellar sample. The sampling parameter is associated with isolating integrals
of the star motion and it is used to build a hierarchical family of subsamples. An accurate
characterisation of the entropy graph is given where a local maximum of entropy takes place
simultaneously with a local minimum 2 error. By working from different sampling parameters
the method is applied to samples from HIPPARCOS and Geneva-Copenhagen survey
(GCS) to obtain kinematic parameters and mixture proportions of thin disk, thick disk and
halo. The sampling parameter P = |(U, V,W)|, absolute heliocentric velocity, allows to build
an optimal subsample containing thin and thick disk stars, by leaving aside most of the halo
population. The sampling parameter P = |W|, absolute perpendicular velocity, is able to
build an optimal subsample containing a mixture of total disk and halo stars, although it
does not allow an optimal segregation of thin and thick disks. Other sampling parameters
like P = |(U,W)| or P = |V | are found to be less population informative. By comparing
both samples, HIPPARCOS provides more accurate estimates for thick disk and halo, while
GCS does for the total disk. In particular, the radial velocity dispersion of the halo fits
perfectly into the empirical Titius-Bode like law U = 6.6 ( 4
3 )3n+2, which was previously proposed
for discrete kinematic components, where the values n = 0, 1, 2, 3 stands for early-type
stars, thin disk, thick disk, and halo populations. Population statistics are used to segregate
thin disk, thick disk, and halo, and to obtain a more accurate bayesian estimation of the
population fractions.
