Thermal iron ions in high speed solar wind streams: Detection by the IMP 7/8 energetic particle experiments

The first measurements of the abundance of iron ions in high speed (> 600 km s−1) solar wind streams have been made with the NOAA/JHU Energetic Particles Experiments (EPE) on IMP 7/8. The identification of iron ions is quantitatively established using 4 years of observations and heavy ion accelerator calibrations of detectors similar to those flown on the spacecraft. Preliminary estimates of the Fe/H ratio are within a factor of 2 of the adopted coronal abundance (5 × 10−5), and there is some evidence that Fe/H may remain approximately constant within a given stream. In the peaks of fast streams (700 < V < 800 km s−1), about 50 iron ion counts are obtained every 20 s, offering the possibility of studying the Fe/H ratio with ∼ 1 m time resolution in high speed streams throughout the decline of Solar Cycle 20 and the rise of Solar Cycle 21.