The Cygnus OB2 association is located in the Galactic Cygnus X region at a distance of 1.4 kpc, making it one of the closest young massive stellar clusters. Cyg OB2 is not only very rich in stellar density but also in its diversity. It is known to contain a rich population of massive stars including almost 2600 OB stars, a large number of binaries (including a collection of some of the most interesting radio emitting colliding-wind binaries), and a considerable number of pre-main sequence stars.
We report here on the first results from The Cyg OB2 Radio Survey (COBRaS), which is a UCL-led e-MERLIN legacy project to provide a deep-field radio mapping of the Cygnus OB2 association. The project has been awarded a total allocation of 252 hours at C-band (5GHz) and 42 hours at L-band (1.6GHz) to image the core of the cluster.
We discuss in particular the presence of non-thermal radio emission at 20 cm (L-band), and its potential as a highly efficient way to identify binaries via single-epoch observations, particularly for colliding-wind binaries. COBRaS data will provide a powerful tool for establishing binary incidence in Cyg~OB2, specifically in the difficult intermediate-period range (1--100~yr). Knowing the binary frequency over the whole period range is important for population synthesis. Additionally, Weak-lined T Tauri (WTT) stars in Cyg OB2 also emit non-thermal radiation from magnetically active regions. Hence these observations will be used to detect the considerable population of younger stars.