An abundance analysis of ROA 24, a likely post-AGB star in Omega Centauri

We present a detailed analysis of high-quality spectra of the F0Ibp star, ROA 24, in ω Cen. The wide spectral coverage allows us to positively identify 28 chemical elements. The C, N, O, Na and s-process elements are significantly enhanced relative to the other giants in ω Cen. The large C abundance implies that 3 α products have been brought to the surface. The amount of s-process element enhancement combined with the relative abundances of the s-process elements in ROA24 requires that 10 per cent of the envelope be composed of material exposed to a neutron exposure of $${\tau }_{0}=0.36$$. We also observe an extreme overdeficiency of A1. Taking all available data together we conclude that ROA24 is either undergoing a blue loop on the upper Asymptotic Giant Branch (AGB) or is already a post-AGB star.