Photometric methods for measuring the metal content of K giants

Correlations are presented between spectroscopically determined ratios of iron-to-hydrogen for K giants and various combinations of color indices. Good correlations are found with the ultraviolet excess of the U, B, V system, two-color differences of the six-color system, one narrow-band system, and one system that combines U, B, V, and six-color indices. Nevertheless, each system has its disadvantages and it is suggested that a four-color system using the 5-20 surface might provide the highest accuracy combined with the greatest efficiency of observing time.