  uvby(--$\beta$) photometry has been obtained for an additional 411 very
metal-poor stars selected from the HK survey, and used to derive basic
parameters such as interstellar reddenings, metallicities, photometric
classifications, distances, and relative ages... These very metal-poor stars
are compared to M92 in the c_0,(b-y)_0 diagram, and evidence is seen for field
stars 1-3 Gyrs younger than this globular cluster. The significance of these
younger very metal-poor stars is discussed in the context of Galactic
evolution, mentioning such possibilities as hierarchical
star-formation/mass-infall of very metal-poor material and/or accretion events
whereby this material has been acquired from other (dwarf) galaxies with
different formation and chemical-enrichment histories

Astrophysics