Bj. Anthonytwarog et al., CN AND CA ABUNDANCE VARIATIONS AMONG THE GIANTS IN M22, Publications of the Astronomical Society of the Pacific, 107(707), 1995, pp. 32-48
Citations number
70
Categorie Soggetti
Astronomy & Astrophysics
Journal title
Publications of the Astronomical Society of the Pacific
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.