Preprint Logo P94 September

To be published in:
Proceedings of the conference on "The Multiwavelength Approach to Unidentified Gamma-Ray Sources", Astrophysics & Space Science (Ap&SS)

On the multiplicity of the O-star CygOB2 #8A and its contribution
to the gamma-ray source 3EG J2033+4118+

M. De Becker1, G. Rauw1,* and J.-P. Swings1

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.


     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.

Key Words
-- stars: individual: CygOB2 #8A -- stars: early-type -- radiation mechanisms: non-thermal

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