S stars in Centauri

The ZrO band at 6473 Å has been found in 10 of the 12 stars previously found to have TiO bands, indicating that these are MS or early S stars. The stars also show strong metal lines and in particular strong Ba IIλ 4554, in common with hotter fainter stars which are also found to lie to the red (cool) side of the giant branch of ω Cen in the I, V–I diagram. These stars are much fainter than MS stars in the Magellanic Clouds and are not associated with carbon stars as the latter are. It is likely that they represent the top of the range of metal abundance in ω Cen and that the strong Ba II and ZrO features result from a primordial excess of s-process elements.