The O V 1213.9 Angstroms forbidden line in the quiet Sun
Curdt, W.; Mathioudakis, M.; Keenan, F. P.; Pinfield, D. J.; Phillips, K. J. H.
United Kingdom, Germany
Abstract
We present the first unambiguous detection of the O v 1213.9 Angstrom (2s(2) (1) S_0 -> 2s2p (3) P_2) forbidden line in the solar spectrum, using observations obtained with the SUMER instrument on board SOHO. The wavelength separation of the forbidden to the (2s(2) (1) S_0 -> 2s2p (3) P_1) intercombination line at 1218.35 Angstroms is 4.5+/-0.1 Angstroms in excellent agreement with theoretical predictions. The observed line ratio, combined with the latest calculations, allows us to derive an electron density of log {N_e/cm(-3}) = 8.5 +/- 0.15 for the quiet Sun. However, the O v 1213.9 Angstroms line was not detected in the HST spectra of Procyon and we can only place a lower limit of log {N_e/cm(-3}) >= 7.8 to the electron density in this object.