On the Evolutionary Status of Extremely Hot Helium Stars - are O(He)   Stars Successors of RCrB Stars?
  95% of all stars end their lives as white dwarfs. About 20% of the hot post-AGB stars are hydrogen deficient. Most of these are the result of a late helium-shell flash, but the evolutionary status of a fraction of about 10-20% of the hottest hydrogen-deficient stars, namely four O(He) stars, is as yet unexplained. They could be the long-searched hot successors of RCrB stars, which have not been identified up to now. If this turns out to be true, then a third post-AGB evolutionary sequence is revealed, which is probably the result of a double degenerate merging process. More generally, understanding details of merging double degenerate stars is of interest in the context of SN Ia events and hence cosmology. 
Thomas Rauch (1 and 2), Elke Reiff (2), Klaus Werner (2), Falk Herwig   (3), Lars Koesterke (4), Jeff W. Kruk (5) ((1) Dr.-R...