Stromgren 4-color photometry of very metal-poor stars

Stromgren uvby photometry has been observed for an additional 140 very meta l-poor stars from the survey of Beers et al. (1992). These Galactic stars o f very-low metallicity provide crucial information for the investigation of the formation and evolution of the Galaxy, as well as on the nature of the early Universe. The Stromgren uvby - beta system allows the measurement of stellar atmospheric parameters as a prelude to detailed abundance studies which will make use of high-resolution spectroscopy and the new generation of large telescopes. The photometric techniques developed by Schuster et al . (1996) are used not only to classify these very metal-poor stars but also to derive effective temperatures, surface gravities, and improved estimate s for their interstellar reddenings. In particular, photometric diagrams su ch as [c(1)], [m(1)] and c(0), (b-y)(0) are used to classify these stars, e specially those near the main-sequence turnoff, where contamination from sl ightly evolved subgiants, lower surface-gravity horizontal-branch stars, an d even a few supergiant or AGB candidates is found.