Implications of Solar Wind Composition for Cometary X‐Rays

Abstract

Solar wind composition provides a strong source of variability for cometary X-rays. Using recently constrained composition observations from the Solar Wind Ion Composition Spectrometer on the Ulysses spacecraft (SWICS/Ulysses) and information on ion-neutral charge-transfer collisions, we model cometary X-ray emission and its variability. Fast and slow solar wind cases are adopted and compared to observations of X-ray spectra from the Röntgen-Satellit (ROSAT) for comet Levy. The predicted and observed spectra compare most favorably for fast solar wind in optically thin conditions. Solar wind composition can be predicted as a function of the coronal temperature near its source and, consequently, cometary X-ray spectra may be predicted as a function of the solar wind's coronal temperature. Implications and additional developments necessary to unravel the compositional information contained in X-ray spectra are explored.