Searching for Wolf-Rayet Stars in M101
  Wolf-Rayet (WR) stars are the evolved descendants of massive O-type stars and are considered to be progenitor candidates for Type Ib/c core-collapse supernovae (SNe). Recent results of our HST/WFC3 survey of Wolf-Rayet stars in M101 are summarised based on the detection efficiency of narrow-band optical imaging compared to broad-band methods. Weshow that on average of 42% WR stars, increasing to ~85% in central regions, are only detected in the narrow-band imaging. Hence, the non-detection of a WR star at the location of ~10 Type Ib/c SNe in broad-band imaging is no longer strong evidence for a non-WR progenitor channel. 
J. L. Bibby, P. A. Crowther, A. F. J. Moffat, M. M. Shara, D. Zurek,   L. Drissen
astro-ph.SR