Cygnus OB2 e-MERLIN 21cm survey (COBRaS)

Based on 42 hours of observations, seven overlapping pointings were employed over multiple epochs during 2014 resulting in 1{sigma} sensitivities down to ~21{mu}Jy and a resolution of ~180mas. A total of 61 sources are detected at 21cm over a ~0.48{deg}x0.48{deg} region centred on the heart of the Cyg OB2 association. Of these 61 sources, 33 are detected for the first time.

We detect a number of previously identified sources including four massive stellar binary systems, two YSOs, and several known X-ray and radio sources. We also detect the LBV candidate (possible binary system) and blue hypergiant star of Cyg OB2 #12. The 21cm observations secured in the COBRaS Legacy project provide data to constrain conditions in the outer wind regions of massive stars; determine the non-thermal properties of massive interacting binaries; examine evidence for transient sources, including those associated with young stellar objects; and provide unidentified sources that merit follow-up observations.

The 21cm data are of lasting value and will serve in combination with other key surveys of Cyg OB2, including Chandra and Spitzer.