The kinematics of 122 red giants and 124 RR Lyrae variables in the solar neighborhood is studied using accurate measurements of their proper motions by the Hipparcos astrometry satellite , combined with the published photometric distances , metal abundances and radial velocities .
A majority of these sample stars have metal abundances with [ Fe/H ] \leq - 1 and thus represent the old stellar populations in the Galaxy .
The halo component with [ Fe/H ] \leq - 1.6 is characterized by no systemic rotation ( < U > , < V > , < W > ) = ( 16 \pm 18 , -217 \pm 21 , -10 \pm 12 ) km s ^ { -1 } and a radially elongated velocity ellipsoid ( \sigma _ { U } , \sigma _ { V } , \sigma _ { W } ) = ( 161 \pm 10 , 115 \pm 7 , 108 \pm 7 ) km s ^ { -1 } .
About 16 % of such metal-poor stars have low orbital eccentricities e < 0.4 , and we see no evidence for the correlation between [ Fe/H ] and e .
Based on the model for the e distribution of orbits , we show that this fraction of low e stars for [ Fe/H ] \leq - 1.6 is explained from the halo component alone , without introducing the extra disk component claimed by recent workers .
This is also supported by no significant change of the e distribution with the height from the Galactic plane .
In the intermediate metallicity range -1.6 < [ Fe/H ] \leq - 1 , we find only modest effects of stars with disk-like kinematics on both distributions of rotational velocities and e for the sample at |z| < 1 kpc .
This disk component appears to comprise only \sim 10 % for -1.6 < [ Fe/H ] \leq - 1 and \sim 20 % for -1.4 < [ Fe/H ] \leq - 1 .
It is also verified that this metal-weak disk has the mean rotation of \sim 195 km s ^ { -1 } and the vertical extent of \sim 1 kpc , which is consistent with the thick disk dominating at [ Fe/H ] = -0.6 to -1 .
We find no metallicity gradient in the halo , whereas there is an indication of metallicity gradient in the metal-weak tail of the thick disk .
The implications of these results for the early evolution of the Galaxy are also presented .