Suprathermal O6+ behavior associated with interplanetary shocks

We report new observations of the behavior of suprathermal O6+ associated with interplanetary shocks. Suprathermal ions are important for understanding the heating and acceleration of plasma throughout the magnetosphere and heliosphere. The Suprathermal Ion Composition Spectrometer (STICS) aboard the Wind spacecraft has been measuring suprathermal ions in the range of 6-230 keV/e for the past 25 years. With its wide, 3.9π steradian field of view (FOV), and ability to fully resolve ion mass and charge, STICS is uniquely capable of producing full 3D velocity distribution functions (VDFs) for a number of ions spanning a range of m/q values, from H through Fe ions. STICS data has been used to study a broad variety of research topics, including the study of solar wind suprathermal tails, general acceleration processes within the heliosphere, and pickup ions from the moon.However, the full potential of STICS has not previously been realized due to the limited publicly available data. We have produced a new, mission-long dataset from STICS that extends the number of analyzed ions across a range of mass and charges and includes 3D VDFs, flow direction histograms, pitch angle distributions, and moments. We present a new analysis of events from this dataset, focused on features in O6+ energy spectra for selected shock-associated periods in the solar wind. These ions are observed transitioning from hot to cold distributions while maintaining isotropy for many shock lengths, until collapsing into a beam coming from the Sun. In other cases, O6+ ions in the same energy range display narrowing, dispersion-like energy distributions while progressing from a wide to a narrow beam. We discuss these observations and relate them to thermal O6+ measured by ACE.