WR-22 - THE MOST MASSIVE WOLF-RAYET STAR EVER WEIGHED

The results of an extensive spectroscopic campaign on the eclipsing bi nary WR22 are presented. A new radial velocity curve is deduced for th e WN7 component, allowing us to improve the parameters of the orbit, f ormerly determined on the basis of photographic spectra. The high sign al-to-noise ratio of our data also allows the detection of some weak a bsorption lines which, for the first time, can definitely be attribute d to the companion. A study of their radial velocities gives a mass ra tio of m(WR)/m(O) = 2.78 leading to a minimum mass of 72M. for the WN7 star. The companion can be classified as a ''late O'' (O6.5-O8.5) sta r with a luminosity ratio of the system q = L(WR)(y)/L(O)(y) at 5500 A ngstrom of about 8. The exceptionally high mass of the WN7 star and it s high hydrogen mass-fraction suggest that WR22 is at the beginning of its Wolf-Rayet evolution. As a matter of fact, with such a high mass, WR22 most probably is still a hydrogen burning object. Therefore, the WN7 component is much closer to a main sequence O star with a ''Wolf- Rayet clothing'' than to the other members of the Wolf-Rayet family, w hich are rather highly evolved He-burning descendants of massive proge nitors.