The investigation of particle-accelerating colliding-wind binaries: a multi-wavelength endeavour

Massive stars are extreme stellar objects whose properties allow for the
study of some interesting physical processes, including particle
acceleration up to relativistic velocities. In particular, the
collisions of massive star winds in binary systems are adequate
environments to accelerate notably electrons involved in synchrotron
emission. This leads to their identification as non-thermal radio
emitters. To date, this has been demonstrated for about 40 objects. The
relativistic electrons are also expected to produce non-thermal
high-energy radiation through inverse Compton scattering. This class of
objects permits thus to investigate non-thermal physics through
observations in the radio and high energy spectral domains. However, the
binary nature of these sources introduces some stringent requirements to
adequately interpret their behavior and model non-thermal processes. In
particular, these objects are well-established variable stellar sources
on the orbital time-scale. The stellar and orbital parameters need to be
determined, and this is notably achieved through studies in the optical
domain. The combination of observations in various spectral domains is
thus the key to investigate these particle-accelerating colliding-wind
binaries, and achieve a clearer view of their role in stellar and
galactic astrophysics.