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We present an empirical s-process abundance distribution derived withexplicit knowledge of the r-process component in the low-metallicity globularcluster M22. We have obtained high-resolution, high signal-to-noise spectra for6 red giants in M22 using the MIKE spectrograph on the Magellan-Clay Telescopeat Las Campanas Observatory. In each star we derive abundances for 44 speciesof 40 elements, including 24 elements heavier than zinc (Z=30) produced byneutron-capture reactions. Previous studies determined that 3 of these stars(the "r+s group") have an enhancement of s-process material relative to theother 3 stars (the "r-only group"). We confirm that the r+s group is moderatelyenriched in Pb relative to the r-only group. Both groups of stars were bornwith the same amount of r-process material, but s-process material was alsopresent in the gas from which the r+s group formed. The s-process abundancesare inconsistent with predictions for AGB stars with M =< 3 Msun and suggest anorigin in more massive AGB stars capable of activating the Ne-22(alpha,n)Mg-25reaction. We calculate the s-process "residual" by subtracting the r-processpattern in the r-only group from the abundances in the r+s group. In contrastto previous r- and s-process decompositions, this approach makes no assumptionsabout the r- and s-process distributions in the solar system and provides aunique opportunity to explore s-process yields in a metal-poor environment.

Characterizing the Heavy Elements in Globular Cluster M22 and an Empirical s-process Abundance Distribution Derived from the Two Stellar Groups