Non-thermal radio emission from O-type stars III. Is Cyg OB2 No. 9 a wind-colliding binary?

S. Van Loo, R. Blomme, S. M. Dougherty +1

The star Cyg OB2 No. 9 is a well-known non-thermal radio emitter. Recent theoretical work suggests that all such O-stars should be in a binary or a multiple system. However, there…