CN AND CA ABUNDANCE VARIATIONS AMONG THE GIANTS IN M22

We have obtained uvbyCa data for over 300 giants and horizontal-branch stars in three fields of M22. The spread in (b-y) for the giant and h orizontal branches is consistent with a spread in foreground reddening Delta E(B-V)similar to 0.08. Reanalysis of the data of Norris and Fre eman (1983a,b) indicates not only positive correlations between CH, CN , and Ca, but decidedly bimodal distributions of CH and CN and a unimo dal distribution for Ca. Our photometric indices, m(1) and hk, demonst rate a range in metallicity that persists to two magnitudes below the horizontal branch, and confirm the correlation between calcium abundan ce and CN/CH. We infer from comparisons to spectroscopic data that m(1 ) is dominated by the CN and CH abundance and find no independent evid ence of a range in [Fe/H]. The excessive ranges in m(1) and hk also su ggest the influence of a continuous opacity source, reminiscent of the Bond-Neff effect, that is correlated with CNO abundance. The relative contributions of internal mixing and primordial variations for M22's giants are discussed.