Radio observations of massive stars

Ronny Blomme

Royal Observatory of Belgium

Detectable radio emission occurs during almost all phases of massive star evolution. I will concentrate on the thermal and non-thermal continuum emission from early-type stars. The thermal radio emission is due to free-free interactions in the ionized stellar wind material. Early ideas that this would lead to an easy and straightforward way of measuring the mass-loss rates were thwarted by the presence of clumping in the stellar wind. Multi-wavelength observations provide important constraints on this clumping, but do not allow its full determination. Non-thermal radio emission is associated with binarity. This conclusion was already known for some time for Wolf-Rayet stars and in recent years it has become clear that it is also true for O-type stars. In a massive-star binary, the two stellar winds collide and around the shocks a fraction of the electrons are accelerated to relativistic speeds. Spiralling in the magnetic field these electrons emit synchrotron radiation, which we detect as non-thermal radio emission. The many parameters that influence the resulting non-thermal radio fluxes make the modelling of these systems particularly challenging, but their study will provide interesting new insight into massive stars.

Reference: "The multi-wavelength view of hot, massive stars", 39th Liège Astrophysical Colloquium, Eds. G. Rauw, M. De Becker, Y. Nazé, J.-M. Vreux, P. Williams, Société Royale des Sciences de Liège, Bulletin, 2011, vol. 80, p. 67-80 (
Status: Conference proceedings