We analyze the high-resolution X-ray spectrum of Hercules X-1 , an intermediate-mass X-ray binary , which was observed with the XMM-Newton Reflection Grating Spectrometer .
We measure the elemental abundance ratios by use of spectral models , and we detect material processed through the CNO-cycle .
The CNO abundances , and in particular the ratio N/O > 4.0 times solar , provide stringent constraints on the evolution of the binary system .
The low and short-on flux states of Her X-1 exhibit narrow line emission from C vi , N vi , N vii , O vii , O viii , Ne ix , and Ne x ions .
The spectra show signatures of photoionization .
We measure the electron temperature , quantify photoexcitation in the He \alpha lines , and set limits on the location and density of the gas .
The recombination lines may originate in the accretion disk atmosphere and corona , or on the X-ray illuminated face of the mass donor ( HZ Her ) .
The spectral variation over the course of the 35 d period provides additional evidence for the precession of the disk .
During the main-on state , the narrow line emission is absent , but we detect excesses of emission at \sim 10–15 Å , and also near the O vii intercombination line wavelength .