P94	September 2004

¹ Institut d'Astrophysique et de Géophysique - Université de Liège, Allée du 6 Août, Bât B5c, B-4000 Liège (Sart Tilman), Belgium

^* Research Associate FNRS, Belgium

⁺ Partly based on observations collected at the Observatoire de Haute Provence, France.

Abstract

     We present the results of an intensive spectroscopic campaign in the optical waveband revealing that CygOB2 #8A is an O6 + O5.5 binary system with a period of about 21.9 d. CygOB2 #8A is a bright X-ray source, as well as a non-thermal radio emitter. We discuss the binarity of this star in the framework of a campaign devoted to the study of non-thermal emitters, from the radio waveband to gamma rays. In this context, we attribute the non-thermal radio emission from this star to a population of relativistic electrons, accelerated by the shock of the wind-wind collision. These relativistic electrons could also be responsible for a putative gamma ray emission through inverse Compton scattering of photospheric UV photons, thus contributing to the yet unidentified EGRET source 3EG J2033+4118.