X-ray lines of helium-like oxygen and neon in the solar corona

The usefulness of the O VII ratio in the study of the nonflaring corona is examined, using data from the SOLEX B spectrometer aboard the USAF P78-1 satellite. The data are consistent with a value of the low-density limit of the photon flux ratio of 3.74 or higher. This range can be considered applicable to nonflare spectra, and is recommended for analyzing all O VII data. The helium-like line ratio G can be used as a probe of the quiet corona between the observer and the emitting active region, and is examined as a plasma diagnostic for both O VII and Ne IX. The value of G in the absence of resonance scattering is determined to be about 1.0 for O VII and about 0.8 for Ne IX.