Wolf-Rayet stars in the Small Magellanic Cloud: II. Analysis of the
  binaries
  Massive WR stars are evolved massive stars characterized by strong mass-loss.
Hypothetically, they can form either as single stars or as mass donors in close
binaries. About 40% of the known WR stars are confirmed binaries, raising the
question as to the impact of binarity on the WR population. By performing a
spectral analysis of all multiple WR systems in the SMC, we obtain the full set
of stellar parameters for each individual component. Mass-luminosity relations
are tested, and the importance of the binary evolution channel is assessed. The
spectral analysis is performed with the PoWR model atmosphere code by
superimposing model spectra that correspond to each component. Evolutionary
channels are constrained using the BPASS evolution tool. Significant Hydrogen
mass fractions (0.1 - 0.4) are detected in all WN components. A comparison with
mass-luminosity relations and evolutionary tracks implies that the majority of
the WR stars in our sample are not chemically homogeneous. The WR component in
the binary AB 6 is found to be very luminous (Log L ~ 6.3 [Lsun]) given its
orbital mass (~10 Msun), presumably because of observational contamination by a
third component. Evolutionary paths derived for our objects suggest that Roche
lobe overflow had occurred in most systems, affecting their evolution. However,
the implied initial masses are large enough for the primaries to have entered
the WR phase, regardless of binary interaction. Together with the results for
the putatively single SMC WR stars, our study suggests that the binary
evolution channel does not dominate the formation of WR stars at SMC
metallicity.
