Clues to the origin of cosmic rays derived from their source composition and energy spectra

Abstract

Cosmic ray composition and energy spectra at source have been recently obtained with good precision. The bulk of the observations suggests that cosmic rays originate in unevolved star surface material. Most cosmic rays should be stellar energetic particles first accelerated by flares out of the Coronae of F to M stars, that got later on reaccelerated to high energy by strong interstellar shock waves. The limitations of this two-step scenario and of the other plausible stellar and interstellar models are pointed out. The 22Ne and carbon excesses at cosmic ray source are accounted for if a minor component (2%) of cosmic rays are made of He-burning material, plausibly originating in Wolf-Rayet stars. The possible oxygen and 25,26Mg excesses could be interpreted in the same context, but not the 29,30Si excess.