Michael R. Collier

The Isotopic Composition of Iron in the Solar Wind: First Measurements with the MASS Sensor on the Wind Spacecraft

The isotopic composition of iron in the solar wind has been measured for the first time with the MASS sensor on the Wind spacecraft. Measurements were made from 1994 December 22 to 1996 February 9 in the energy range 0.55-1.3 keV nucleon-1 (320-500 km s-1). We obtained the values 54Fe/56Fe = 8.5+ 0.5−2.2% and 57Fe/56Fe ≤ 5%. Previously, measurements were reported for meteoritic material (e.g., Anders & Grevesse 1989,54Fe/56Fe = 6.3% and 57Fe/56Fe = 2.3%) and the origin of Galactic cosmic rays (e.g., Connell & Simpson 1995,54Fe/56Fe = 8.9% ± 0.8% and 57Fe/56Fe = 3.8% ± 0.5%).

Helioradius Dependence of Interplanetary Carbon and Oxygen Abundances during 1991 Solar Activity

A comparison of the heliocentric dependence of the relative abundance of low energy (~1 MeV nucleon-1) carbon and oxygen on the Ulysses (~3-4 AU) and Voyager 1 and 2 (~35 and ~47 AU) spacecraft shows that the C/O abundance ratio is significantly smaller at the larger radial distances. This finding is attributed to a more abundant seed population for anomalous cosmic-ray oxygen than for carbon in the outer solar system, where the seed population can be accelerated by shocks in global merged interaction regions. The energy spectra of carbon and oxygen at the different locations are approximately the same.