Where does the disk stop and the halo begin? Kinematics in a rotation field

A sample of G and K giants, approximately 4 kpc away from the sun, covering the abundance range from disk to halo in a field chosen to measure rotational kinematics, is discussed. To study the disk to halo transition, the sample has been enlarged with similar samples of stars in the solar neighborhood to include almost 200 giants and the concept of 'thick disk' has been introduced. For selected giants, abundances, distances, and reddenings are derived, and velocity dispersion is estimated. From the data presented, it is concluded that the disk and halo abundance distributions overlap and that their kinematics are discontinuous. The kinematics of the metal-weak red giants, with abundances extended as low as Fe/H = -1.6, is compared with the kinematics of the halo objects, and the data are interpreted with respect to the thick disk, the halo kinematics, and the theories of galaxy formation.