2021MNRAS.503.2514B

We present a deep radio-polarimetric observation of the stellar bow shock EB27 associated with 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 (2-4 GHz) to test whether this synchrotron emission is polarized. 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 polarization is detected in the bow shock above 0.5 per cent, although we detected polarized emission from two southern sources, probably extragalactic in nature. We modelled 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.