LARGE IRAS SHELLS AROUND GALACTIC WOLF-RAYET STARS AND TYPE-O STAR PHASE OF WOLF-RAYET EVOLUTION

We present IRAS Skyflux images of the environments of galactic Wolf-Ra yet stars. These form a complete sample of all galactic Wolf-Rayet sta rs of the van der Hucht et al. (1981) catalog observed by IRAS, a tota l of 156 stellar environments. The intent of this survey is to obtain information on the large bubbles expected from the early O star phase of Wolf-Rayet stars. A total of 49 probable or suspected shells of >20 ' in diameter have been observed in our data, with a detection rate of 60% for large IRAS shells around Wolf-Rayet stars at galactic latitud es >2 degrees. Fourteen of the IRAS shells are associated with previou sly observed, slowly expanding HI bubbles. Most shells are unlikely to be due to line-of-sight coincidence, although two shells may be assoc iated with foreground or background supernova remnants. In considering the origin of the shells we indicate that most are unlikely to have f ormed from the explosion of a binary companion to a Wolf-Rayet star an d that few, if any, are Likely to be associated with ejecta produced i n a Roche Lobe overflow. The sizes of the shells, together with their known or estimated expansion velocities ate consistent with the estima tes of the period of the O star progenitor phase calculated in evoluti onary models of single WR stars. (C) 1996 American Astronomical Societ y.