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Winds from massive stars have recently been deemed promising sites forinvestigating relativistic particle acceleration. Particularly, the resultingbow shock from the interaction of the winds of runaway stars with interstellarmatter has been observed at multiple wavelengths. Here we investigate the O4Ifstar, BD+433654, the bow shock of which is, so far, the only one proven toradiate both thermally and non-thermally at radio frequencies. We also considerNGC7635 as a bow shock candidate and examine its apex for indications ofthermal and non-thermal radio emission. We observed both sources with the VLAat 4-8 GHz and 8-12 GHz, and with the Effelsberg telescope at 4-8 GHz. Weanalysed data from both telescopes individually and combined, obtained theirspectral index maps and calculated their Spectral Energy Distributions. Wepresent the first high-resolution maps of radio emission from NGC7635. We findthat both emit non-thermal emission in the radio regime, with the clearestevidence for NGC7635. Our results are less conclusive for BD+433654, as theemission from its bow shock becomes weaker and fainter at higher radiofrequencies. Our results extend the previous radio results for the BD+433654bow shock to higher frequencies. Modelling of our data for both sources showsthat accelerated electrons at the wind termination shock are a plausible sourcefor the non-thermal radio emission, but energetics arguments suggest that anynon-thermal X-ray and $\gamma$-ray emission could be significantly belowexisting upper limits. Enhanced synchrotron emission from compressed Galacticcosmic rays in the radiative bow shock could also explain the radio emissionfrom the BD+433654 bow shock but not NGC7635. Non-detection of point-like radioemission from BD+433654 puts an upper limit on the mass-loss rate of the starthat is lower than values quoted in the literature. [abridged]

And then they were two: detection of non-thermal radio emission from the bow shocks of two runaway stars