A search for stars of very low metal abundance. IV. uvbyCa observations ofmetal-weak candidates from the northern HK survey

CCD photometry on the uvbyCa system has been obtained for 521 candidate met al-poor stars from the northern hemisphere KK survey of Beers and colleague s. Reddening corrections, classifications of stars by luminosity class, and the derivation of metal abundances based on Stromgren indices m(1) and hk are described and presented, along with preliminary spectroscopic estimates of abundance. A number of extremely metal-poor stars with [Fe/H] less than or equal to -2.50 are identified.