| Stellar populations provide important clues to the evolution of the Milky Way. We report the results of two surveys of late-type stars aimed at understanding the nature (dynamics, chemistries) of the disk and halo Galactic stellar populations.; We study the kinematical properties of 303 late-type dwarfs out to ∼6 kpc at the North Galactic Pole (NGP) as derived from deep (V ∼22), high precision (.001" yr-1) proper motions by Majewski (1992) combined with new deep CCD photometry, which yield photometry parallaxes needed to convert the proper motions to U and V space motions. A clear disk population to Z ∼3 kpc can be discerned with a strong asymmetric drift gradient of -46+/-4 km s-1 kpc-1. Halo dwarfs dominate over the thick disk at Z ∼3 kpc. In addition to the strong signal of disk stars, a retrograde halo moving group is identified in the U - V plane that is likely the same as the moving group detected at the NGP by Majewski (1992).; We have also obtained medium resolution (2-4 A) spectra for 749 late K and early M giants at mid-latitudes selected from the 2MASS catalog with the FOBOS system at Fan Mountain Observatory. These spectra provide radial velocities (RVs) at the 5 km s-1 level, spectroscopic [Fe/H] good to sigma=0.25 dex, and information on the relative abundances of Mg/Fe and Na/Fe in these stars. The UCAC2 proper motions and RVs yield full stellar space motions. We find ail asymmetric drift for the thin/thick disk of -26+/-4 kill s-1 kpc -1, significantly smaller than that found for the M dwarf sample above. We attribute the difference to purity of sample in that M giants are not found in the halo field except in readily identifiable halo substructures.; Based on the lack of a vertical gradient in the [alpha/Fe]-[Fe/H] patterns and the strong vertical gradient in rotational velocity for both of our surveys, we conclude that our findings support a most likely formation scenario in which the thick disk was formed by the heating of the early disk due to a merger. |
