Solar Wind Charge Exchange

Within the solar system, the solar wind charge exchange (SWCX) process can produce time-variable X-ray foreground emission. The hot solar wind can pick up electrons from the neutral medium in the solar system, capturing them into excited energy levels rarely populated in other mechanisms (e.g., collisional ionization equilibrium, photoionization equilibrium). The unstable excited energy level is de-populated by line emissions. The characteristic features of SWCX are the enhanced forbidden line of the He-like triplet with respect to the resonance line and the enhanced high-order Lyman series line with respect to the Lyα line. High-resolution X-ray spectroscopy is the key to quantifying the role of SWCX in such kind of X-ray foreground emission.