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D. J. Wallace, D. R. Gies (CHARA), E. Nelan, C. Leitherer (STScI)
Two separate models have been proposed to explain the non-thermal emission detected in some Wolf-Rayet (WR) stars. In models based on single WR stars, this emission is proposed to arise via synchrotron radiative processes in the outer (intrinsically unstable) WR wind (e.g. White & Chen 1995). In models based on WR~+~O systems, this non-thermal radio emission is suggested to arise from the WR wind colliding with the wind of a companion (e.g. Williams et al.\ 1990). In order to be observed, the colliding winds region is believed to occur in wide binaries where the interaction zone is outside the WR radio photosphere (\approx30~AU based on spherically symmetric uniform wind models).
HST FGS1R observations of 9 non-thermal and 9, as a
control group, purely thermal radio emitting stars attempted
to verify the theory that this non-thermal emission is
always a result of binary interactions. If the binary model
is correct, then most or all of our non-thermal targets
should have companions with projected separations of
0\farcs01 Support for this work was provided by NASA through grant
number GO-8309 from the Space Telescope Science Institute,
which is operated by AURA, Inc., under NASA contract
NAS5-26555.