Abundances in Three Heavy-Element Stars in $\omega$ Centauri

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Session 50 -- Globular Clusters
Display presentation, Wednesday, 9:20-6:30, Pauley Room

[50.09] Abundances in Three Heavy-Element Stars in $\omega$ Centauri

Andrew D. Vanture, George Wallerstein, Jeffery A. Brown (University of Washington)

The abundances of the iron-peak elements Fe, Ni and Ti, the $\alpha$ elements Mg, Al and K and the s-process elements Rb, Y and Zr are determined for the heavy-element stars ROA 371, ROA 5293 and ROA 3812 in the globular cluster $\omega$ Centauri. ROA 3812 and ROA 5293 are classified as S stars while ROA 371 is classified as a barium star. The metallicities of ROA 3812, 5293 and 371 are [Fe/H]=-0.7, -1.0 and -1.5 respectively. This places ROA 371 in the middle of the range of metallicities found for giant branch stars in $\omega$ Cen by Brown et al. (1991, A\&A, 249, L13). However, both ROA 3812 and 5293 have metallicities near the upper end of the range for the cluster. This result is in agreement with the interpretation of the positions of these three stars in the color-magni tude diagram of $\omega$ Cen made by Lloyd Evans (1983, MNRAS, 204, 975). We find no significant evidence for enhancements of Mg and K relative to other stars in $\omega$ Cen but do find evidence for enhancements of Al. Enhancements of the s-process elements in these stars are approximately 10 to 25 relative to solar. An analysis of the Rb/Y and Rb/Zr abundances indicate these elements were formed in an environment with a neutron density greater than 10$\rm ^8$ cm$\rm ^{-3}$.

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