H and He-like Ions Emission in the Spectra of X-ray Binaries.

We study the emission from H and He-like ions, particularly oxygen and neon, observed in ASCA spectra of low-mass X-ray binaries (LMXBs). The observed strengths of these lines relative to the recombination continua seem to differ from the classic recombination model. This suggests a different excitation mechanism for the lines. Various mechanisms, including collisional excitation, continuum resonance fluorescence and three body recombination, are discussed.