A Search for Stars of Very Low Metal Abundance. IV. UVBYCA Observations of Metal-weak Candidates from the Northern HK Survey

CCD photometry on the uvbyCa system has been obtained for 521 candidate metal-poor stars from the northern hemisphere HK survey of Beers and colleagues. Reddening corrections, classifications of stars by luminosity class, and the derivation of metal abundances based on Strömgren indices m₁ and hk are described and presented, along with preliminary spectroscopic estimates of abundance. A number of extremely metal-poor stars with [Fe/H]<=-2.50 are identified.