ABUNDANCES IN 3 HEAVY-ELEMENT STARS IN OMEGA-CENTAURI

The abundances of the iron-peak elements Fe, Ni, and Ti, the light met als Mg, Al, and K, and the s-process elements Rb, Y, and Zr are determ ined for the heavy-element stars ROA 371, ROA 5293, and ROA 3812 in th e globular cluster Omega Centauri. ROA 3812 and ROA 5293 are classifie d as S stars while ROA 371 is classified as a K5 barium star. The meta llicities of ROA 3812, 5293, and 371 are [Fe/H]= -0.7, -0.8, and - 1.0 , respectively. Thus, ROA 371 has a metallicity slightly higher than t he red giants analyzed by Brown et al. (1991) and ROA 3812 and 5293 ha ve metallicities near the upper end of the range for the cluster. All three stars show an excess of Al, which is common in red giants of Ome ga Centauri, and a mean excess of the s-process elements Rb, Y, and Zr of 1.4 dex. In addition, all three stars are too faint to be asymptot ic giant branch (AGB) stars according to cur-rent theory. Hence, they were either formed with their present composition, as suggested by Llo yd Evans (1983a) or are binaries that have had their atmospheres pollu ted by a now defunct companion. Based upon the dependence of [s/Fe] on [Fe/H] for various s-process elements over a range from [Fe/H] = - 2. 0 to [Fe/H] = - 0.7, we show that the Lloyd Evans hypothesis is probab ly correct. This shows that mass loss from AGB stars was contributing s-process elements to the intracluster gas for as much as 10(9) yr bef ore Type Ia SNe swept the cluster clear of gas and terminated star