The properties of single WO stars
  The enigmatic oxygen sequence Wolf-Rayet (WO) stars represent a very late stage in massive star evolution, although their exact nature is still under debate. The spectra of most of the WO stars have never been analysed through detailed modelling with a non-local thermodynamic equilibrium expanding atmosphere code. Here we present preliminary results of the first homogeneous analysis of the (apparently) single WOs. 
F. Tramper, S.M. Straal, G. Gr\"afener, L. Kaper, A. de Koter, N.   Langer, H. Sana and J.S. Vink
astro-ph.SR