2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/104193Two evolutionary scenarios are proposed for the formation of extreme helium stars: a post-AGB star suffering from a late thermal pulse, or the merger of two white dwarfs. An identification of the evolutionary channel for individual objects has to rely on surface abundances. We present preliminary results from a non-LTE analysis of CNO, Mg and S for two unique objects, V652 Her and HD144941. Non-LTE abundance corrections for these elements range from negligible values to ~0.7 dex. Non-LTE effects typically lead to systematic shifts in the abundances relative to LTE and reduce the uncertainties.4 pages, 2 figures; to appear in: Baltic Astronomy, Proceedings of the Second Meeting on Hot Subdwarf Stars an Related Objects, La Palma, June 2005Astrophysicstext