Deriving Pickup Ion Properties from Ulysses SWICS Observations

Integrating the particle spectra of ions in the solar wind (SW) allows for the determination of the bulk plasma properties, such as the density and temperature, of interstellar pickup ions (PUIs). These results are important for validating simulations of the interaction between the SW and the local interstellar medium (LISM), as including the effects of interstellar PUIs in these simulations can significantly modify the outer heliospheric boundaries. We build on the particle spectra from Zhang et al. (2019), which are generated from measurements made by the Solar Wind Ion Composition Spectrometer (SWICS) instrument on the Ulysses spacecraft with a new method of converting the particle distribution functions from the spacecraft frame to the SW frame. This approach offers an improvement upon the standard narrow-beam approximation. We calculate the moments of these particle spectra to determine the bulk plasma properties of the interstellar PUIs, in particular pickup protons (H+) and pickup Helium (He+). We compare our pickup proton density and temperature results to those in Intriligator et al. (2012), where the particle spectra are converted to the SW frame using the narrow-beam approximation. Our results are given for six-hour intervals over two months during the Halloween 2003 solar storms. In general, our PUI density is higher than that calculated in Intriligator et al. (2012). Additionally, we chose one of many shocks during the solar event period to analyze. We determined the bulk SW properties from the Solar Wind Observations Over the Poles of the Sun (SWOOPS) instrument as well as the PUI properties from the particle spectra ahead and behind the shock. Our results are promising for the purpose of studying interstellar PUIs during quiet times as well as during solar events. The results of this analysis can be used to validate heliospheric simulations relevant for space weather predictions.