Implications for source populations of energetic ions in co-rotating interaction regions from ionic charge states Available to Purchase

The ionic charge states of He have been observed in several co-rotating interaction regions (CIR) in 1999 and 2000 with ACE SEPICA. For all CIRs under study the $He+/He2+$ ratio increases consistently from the start of the event towards the end, while the absolute flux of the energetic ions usually reaches a maximum close to the beginning of the event. With time, the spacecraft is magnetically connected to the compression region at increasing distance from the sun. Therefore, the increasing $He+/He2+$ ratio can be interpreted as an increase in the relative importance of interstellar pickup ions over the solar wind as a source for the energetic ions. In addition, the observed $He+/He2+$ ratio and its increase with the inferred distance from the sun provide an estimate of the injection and acceleration efficiencies for these species, which is found to be higher by about two orders of magnitude for pickup ions compared with the solar wind.