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 A spectral survey, I found the emission line of the forbidden coronal transition of Fe XIII at λ = 10,747A. This line (3P1–3P0) is often accompanied by the 3P2–3P1 line at λ = 10,798 A at high densities (Ne > 109). The emission line λ = 10,747 A 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 A and Pγ as well as a line at 11,013 A 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 A and 6,374 A (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-A line definitely absent. If the lines are excited by the 2,400-K radiation field of the star, the 6,374-A and 5,303-A lines should be much fainter than the 10,747-A, because of their higher excitation energy.