Charge exchange between highly charged ions and atomic H for modelling comet C/1999 S4 X-ray emission

Solar wind (SW) charge exchange (CX) is an important mechanism responsible for X-ray emissions in comets' coma and many other astrophysical environments. By incorporating the experimentally derived total cross-sections and the tested state-selectivity models into the Kronos program, we generate X-ray spectra in H-like and fully stripped C, N, O ion CX collision with atomic H. Using these data, we revisit the fitting of Chandra X-ray data of Comet C/1999 S4 by considering the typical SW collision energies of 0.8 and 3 keV/u, respectively. Our results are in an excellent agreement with the astrophysical observation. We find that charge exchange between C-5+,C-6+, N-6+,N-7+, O-7+,O-8+ and H significantly contributes to the comet's spectrum ranging from 300 to 800 eV for both slow and fast SW ions, where N7+ abundance is underestimated in previous studies.