a1 Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussels, Belgium, email: email@example.com
a2 Institut d'Astrophysique, Université de Liège, Allée du 6 Août, 17, Bât B5c, B-4000 Liège (Sart-Tilman), Belgium
a3 Observatoire de Haute-Provence, F-04870 Saint-Michel l'Observatoire, France
Some OB stars show variable non-thermal radio emission. The non-thermal emission is due to synchrotron radiation that is emitted by electrons accelerated to high energies. The electron acceleration occurs at strong shocks created by the collision of radiatively-driven stellar winds in binary systems. Here we present results of our modelling of two colliding wind systems: Cyg OB2 No. 8A and Cyg OB2 No. 9.