Fe XIII line in R Aquarii

Abstract

GREGORY and Seaquist¹ have detected radio emission from the interesting object R Aquarii². In the course of reducing plates of this star made in 1970 and 1971 in the course of my He I, λ = 10,830 Å spectral survey, I found the emission line of the forbidden coronal transition of Fe XIII at λ = 10,747Å. This line (³P₁–³P₀) is often accompanied by the ³P₂–³P₁ line at λ = 10,798 Å at high densities (N_e > 10⁹). The emission line λ = 10,747 Å is weak, but clearly seen on two spectra (Fig. 1), with intensity of ∼ 100 mA. The spectrum also shows strong emission lines of He I at 10,830 Å and Pγ as well as a line at 11,013 Å which may be He I 3¹S–6¹P. I have examined an old plate made by Merrill in 1948 for traces of the coronal lines at 5,303 Å and 6,374 Å (Fe XIV and Fe X) and found them absent. G. Wallerstein (personal communication) has kindly examined his plates from 1970–71 and finds the 6,374-Å line definitely absent. If the lines are excited by the 2,400-K radiation field of the star, the 6,374-Å and 5,303-Å lines should be much fainter than the 10,747-Å, because of their higher excitation energy.