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Paper: Non-Thermal Radio Emission from ‘Presumably’ Single O Stars
Volume: 422, High Energy Phenomena in Massive Stars
Page: 157
Authors: Van Loo, S.
Abstract: A number of hot stars have radio fluxes that deviate from a simple thermal spectrum. It is generally accepted that synchrotron radiation from relativistic particles accelerated in shocks, can account for this non-thermal radio emission. A fundamental question regarding non-thermal radio emission is its correlation with binarity. For Wolf Rayet stars, the evolutionary descendents of O stars, this link is already well established, i.e. a binary component seems to be a pre-requisite for non-thermal radio emission. For binaries, the shocks needed for the acceleration of the electrons arise where two (or more) stellar winds collide. Roughly two thirds of the non-thermal O stars are confirmed binary or multiple systems. For the other stars, binarity has not been established. In these ‘presumably’ single stars, shocks are ubiquitous due to the instability of the radiative driving mechanism of the stellar wind. Recent theoretical studies however show that this embedded-shock model cannot be the source of the non-thermal emission and that the accelerating shocks arise where two stellar winds collide. This conclusion implies that all non-thermal emitting O stars are in a binary system. New observational evidence seem to corroborate this binary scenario.
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