The Wolf-Rayet Content of M31
  Wolf-Rayet stars are evolved massive stars, and the relative number of
WC-type and WN-type WRs should vary with the metallicity of the host galaxy,
providing a sensitive test of stellar evolutionary theory. However, past
studies of the WR content of M31 have been biased towards detecting WC stars,
as their emission line signatures are much stronger than those of WNs. Here we
present the results of a survey covering all of M31's optical disk (2.2 deg^2),
with sufficient sensitivity to detect the weaker-lined WN-types. We identify
107 newly found WR stars, mostly of WN-type. This brings the total number of
spectroscopically confirmed WRs in M31 to 154, a number we argue is complete to
~95%, except in regions of unusually high reddening. This number is consistent
with what we expect from the integrated Halpha luminosity compared to that of
M33. The majority of these WRs formed in OB associations around the Population
I ring, although 5% are truly isolated. Both the relative number of WC to
WN-type stars as well as the WC subtype distribution suggest that most WRs
exist in environments with higher-than-solar metallicities, which is consistent
with studies of M31's metallicity. Although the WC-to-WN ratio we find for M31
is much lower than that found by previous studies, it is still higher than what
the Geneva evolutionary models predict. This may suggest that Roche-lobe
overflow produces the excess of WC stars observed at high metallicity, or that
the assumed rotational velocities in the models are too high.
