Elemental Source Composition Measurements and the Origin of Galactic Cosmic Rays

Abstract

We present measurements of the elemental abundances of ultra-heavy (Z>29) cosmic rays made by the CRIS instrument on NASA’s ACE satellite. The data set corresponds to 7406 days of data collection from December 4, 1997 through Feb. 18, 2019. We detected a total of 1205 ultra-heavy nuclei in the charge range of Z=30-40. The charge resolution that we obtain shows essentially complete separation of the elements over this charge range. We derive preliminary source abundances from these measurements. These source abundances show that the ordering of refractory and volatile elements with atomic mass is greatly improved when compared to a mix of massive star outflow plus SN ejecta with normal ISM, rather than with only normal ISM. Additionally, in this ordering the refractory and volatile elements have similar slopes and refractory elements are preferentially accelerated by a factor of ~4. The measured abundances support a model in which cosmic ray source material is a mix of massive star outflow plus supernova ejecta and normal ISM, consistent with conclusions reached from the SuperTIGER high-altitude balloon measurements.