SOLAR CORONAL AR/FE AND NE/MG ABUNDANCE RATIOS DERIVED FROM ULTRAVIOLET FORBIDDEN LINE SPECTRA

Solar spectra of forbidden lines of Mg V, Ar XI, Ca XV, Fe XII, and the absence of a Ne V line are used to determine the Ar/Fe abundance ratio, and an upper limit for the Ne/Mg abundance ratio, in solar coronal active regions. The derived abundance ratios of Ar/Fe are 3.1 × 10-2 ± 35% and Ne/Mg ≤ 0.4. The forbidden lines occur at wavelengths: Mg V, 1324.45 Å; Fe XII; 1349.38 Å, Ca XV, 1375.98 Å; Ar XI, 1392.12 Å. The unobserved Ne V line is predicted to fall at 1574.68 Å. The spectra were recorded by the Naval Research Laboratory S082-B slit spectrograph flown on the Skylab manned space station. The derived abundance ratios are consistent with lower abundances of Ne and Ar in the corona relative to low first ionization potential elements (such as Mg, Fe, and Ca), than is derived for the solar photosphere, i.e., from local galactic abundances.