On the origin and composition of Galactic cosmic rays

Context. The composition of Galactic cosmic rays (GCR) presents strong similarities to the standard (cosmic) composition, but also noticeable differences, the most important of which is the high isotopic ratio of Ne-22/Ne-20, which is similar to 5 times higher in GCR than in the Sun. This ratio provides key information on the GCR origin. Aims. We investigate the idea that GCR are accelerated by the forward shocks of supernova explosions, while they run through the pre-supernova winds of the massive stars and through the interstellar medium. Methods. We use detailed wind and core yields of rotating and non-rotating models of massive stars with mass loss, as well as simple models for the properties of the forward shock and of the circumstellar medium. Results. We find that the observed GCR Ne-22/Ne-20 ratio can be explained if GCR are accelerated only during the early Sedov phase, for shock velocities >1600 km s(-1). The acceleration efficiency is found to be of the order of 10(-6)-10(-5), i.e. a few particles out of a million encountered by the shock escape the SN at GCR energies. We also show quantitatively that the widely publicized idea that GCR are accelerated in superbubbles fails to account for the high Ne-22/Ne-20 ratio in GCR.