Gemini GMOS spectroscopy of HeII nebulae in M33
  We have carried out a narrow-band survey of the Local Group galaxy, M33, in
the HeII4686 emission line, to identify HeII nebulae in this galaxy. With
spectroscopic follow-up observations, we confirm three of seven candidate
objects, including identification of two new HeII nebulae, BCLMP651, HBW673. We
also obtain spectra of associated ionizing stars for all the HII regions,
identifying two new WN stars. We demonstrate that the ionizing source for the
known HeII nebula, MA 1, is consistent with being the early-type WN star MC8
(M33-WR14), by carrying out a combined stellar and nebular analysis of MC8 and
MA1. We were unable to identify the helium ionizing sources for HBW 673 and
BCLMP 651, which do not appear to be Wolf-Rayet stars. According to the
[OIII]5007/Hbeta vs [NII]6584/Halpha diagnostic diagram, excitation mechanisms
apart from hot stellar continuum are needed to account for the nebular emission
in HBW 673, which appears to have no stellar source at all.
