Observational and Evolutionary Aspects of Wolf-Rayet Stars

Many authorities proclaimed that all WR stars are members of close binary systems with OB type companions (see e.g. I.A.U. Symp.n°43). Arguing that fainter stars were less well studied Kuhi (1973) only considered northern systems brighter than mv=10m. In this sample 73% of the WR stars are binary components. Due to the very low disruption pro­ bability during the supernova explosion of the low mass component in a massive binary (De Cuyper et al. , 1976) classical evolutionary theory predicts that there should be as many WR+OB type systems as there are WR+compact star systems (de Loore et al . , 1975). If 73% WR+OB systems would be real, the evolutionary predictions would give serious problems. Fortunately, the proposed 73% is proba­ bly largely overestimated. P.S. Conti made spectra with the 4m telescopes at the observatories of Kitt Peak and Cerro Tololo of nearly all the galactic WR stars and those in the LMC studied by Smith (1968). One of the important results to remember here is that very few additional stars were found to have absorption lines that had not been listed as such by Smith already. On the other hand, the mv of many of the brightest WR stars is dominated by a companion. In the fainter WR stars the continuum is dominated by the WR star itself. Therefore if one decides only to consider systems brighter than mv=10m one preferentially includes the binaries and this biases the statistics. The new measurements show a binary frequency ~40(±10)% for the Galaxy and for the LMC considering the whole sample now and using the criterion : binary means absorption lines present.