  We present a deep radio-polarimetric observation of the stellar bow shock
EB27 associated to the massive star BD+43 3654. This is the only stellar bow
shock confirmed to have non-thermal radio emission. We used the Jansky Very
Large Array in S band (2 - 4GHz) to test whether this synchrotron emission is
polarised. The unprecedented sensitivity achieved allowed us to map even the
fainter regions of the bow shock, revealing that the more diffuse emission is
steeper and the bow shock brighter than previously reported. No linear
polarisation is detected in the bow shock above 0.5%, although we detected
polarised emission from two southern sources, probably extragalactic in nature.
We modeled the intensity and morphology of the radio emission to better
constrain the magnetic field and injected power in relativistic electrons.
Finally, we derived a set of more precise parameters for the system EB27-BD+43
3654 using Gaia Early Data Release 3, including the spatial velocity. The new
trajectory, back in time, intersects the core of the Cyg OB2 association.
