Description:
New observations of the colliding wind Wolf-Rayet WC7+O4-5 binary WR140 (HD 193793) at 6 cm and 21 cm with the Westerbork Synthesis Radio Telescope are presented. They show that the 21 cm flux, in particular, rose to a sharp maximum in 1992, lagging about a year behind the 6 cm flux. After maximum, both fell simultaneously. The data are interpreted in terms of the varying circumstellar extinction to a non-thermal source in the wind interaction region due to the winds of both WC and O stars.