Discovery of an ''alpha'' element-poor halo star in a search for very low-metallicity disk stars

We report [Fe/H] results for a sample of five high-velocity metal-poor halo population stars and five comparably metal-poor stars thought to have kinematics typical of an older, hotter disk population. We also derive abundances of lithium, oxygen, magnesium, silicon, calcium, titanium, and barium for many of the stars. Four of the candidate disk population stars are found to be subgiants, and a re-evaluation of their kinematics show that they have kinematics typical of the halo population. One star, G190-25, is confirmed to be a dwarf with thick disk-like kinematics: U=-10, V=-80, W=-90 km s(-1). It is indistinguishable in [X/Fe] from other metal-poor stars with higher velocities, however. The most interesting star is the high-velocity subgiant BD+80 degrees 245, which is found to have [[''alpha''/Fe]]=-0.29+/-0.02 despite its low metallicity, [Fe/H]=-1.86. It is also extremely deficient in barium, [Ba/Fe]approximate to-1.8, and has a large apogalacticon distance, over 20 kpc. It has experienced a very different chemical history than have other metal-poor stars found in the solar neighborhood. (C) 1997 American Astronomical Society.