Wolf-Rayet stars in M81: Detection and Characterization using GTC/OSIRIS
  spectra and HST/ACS images
  We here report the properties of Wolf-Rayet (W-R) stars in 14 locations in
the nearby spiral galaxy M81. These locations were found serendipitously while
analysing the slit spectra of a sample of ~150 star-forming complexes, taken
using the long-slit and Multi-Object spectroscopic modes of the OSIRIS
instrument at the 10.4-m Gran Telescopio Canarias. Colours and magnitudes of
the identified point sources in the Hubble Space Telescope images compare well
with those of individual W-R stars in the Milky Way. Using templates of
individual W-R stars, we infer that the objects responsible for the observed
W-R features are single stars in 12 locations, comprising of 3 WNLs, 3 WNEs, 2
WCEs and 4 transitional WN/C types. In diagrams involving bump luminosities and
the width of the bumps, the W-R stars of the same sub-class group together,
with the transitional stars occupying locations intermediate between the WNE
and WCE groups, as expected from the evolutionary models. However, the observed
number of 4 transitional stars out of our sample of 14 is statistically high as
compared to the 4% expected in stellar evolutionary models.
