Authors: Gabriel Muro (Caltech), Christina Cohen (Caltech), Rick Leske (Caltech), Zigong Xu (Caltech), Eric Christian (NASA GSFC), Grant Mitchell (NASA GSFC), Maher Dayeh (SwRI), Mihir Desai (SwRI), Keiichi Ogasawara (SwRI), Matina Gkioulidou (JHU APL), Drew Turner (JHU APL), David McComas (Princeton University)
Mason et al. (2012) showed that the apparent time dependence of heavy-ion abundance ratios in SEP events may be caused by how particles propagate through space, rather than by changes at the source. When they compared ions by rigidity instead of energy per nucleon, the abundance ratios became more stable. However, that approach required assuming charge states as a key limiting factor.
The Interstellar Mapping and Acceleration Probe’s (IMAP) energetic particle instruments now allow this test to be revisited with measured charge-state information. CoDICE-Lo provides suprathermal charge-state measurements that can be used to estimate Q/M in the pre-accelerated seed population, while CoDICE-Hi and HIT provide the higher-energy composition needed to compare abundance ratios such as Fe/O as a function of both energy per nucleon and rigidity.
Using early IMAP SEP events, we examine whether Fe/O, C/O, or He/O smoothly vary across the suprathermal to SEP transition, and whether they are more constant when organized by rigidity or by energy per nucleon. By utilizing measured suprathermal charge-states rather than assuming values, this work better examines the degree to which interplanetary transport affects SEP abundances at 1 AU.