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| Paper: |
Multiple Histories Among the Metal-poor Field and Cluster Stars |
| Volume: |
92, Formation of the Galactic Halo. . . . Inside and Out |
| Page: |
103 |
| Authors: |
Carney, Bruce W. |
| Abstract: |
The kinematics and metallicities of a large sample of local proper motion stars reveal several components among the metal-poor stars. One that dominates at large distances from the plane shows younger ages, no radial metallicity gradient, and a net retrograde rotation, all consistent with an accreted population. Another, that dominates closer to the plane, has an older mean age, net prograde Galactic rotation, and a weak radial metallicity gradient, consistent with a dissipative origin and perhaps the beginnings of the Galactic disk. The intermediate-age, metal-poor population identified by Preston et al. (AJ, 108, 538, 1994) is also seen in the data. There may be substructure in the V velocity vs. apogalacticon plane, indicative of multiple merger events. Contrary to common conceptions, the halo population(s), as manifested by the globular clusters, do not show any sign of contributions from SNe Ia events. [O/Fe] and [alpha /Fe] are constant over wide ranges in [Fe/H] and age. Either the SN Ia timescale is very long, or the classes of globular clusters, ``old halo", ``young halo", and ``disk", have not shared common chemical histories, perhaps due to accretion by the Galaxy of at least one of them. |
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