The O v 1213.9 angstrom forbidden line in the quiet Sun

We present the first unambiguous detection of the O V 1213.9 Angstrom (2s(2 ) S-1(0) --> 2s2p P-3(2)) forbidden line in the solar spectrum, using obser vations obtained with the SUMER instrument on board SOHO. The wavelength se paration of the forbidden to the (2s(2) S-1(0) --> 2s2p P-3(1)) intercombin ation line at 1218.35 Angstrom is 4.5 +/- 0.1 Angstrom in excellent agreeme nt 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 Angstrom lin e was not detected in the HST spectra of Procyon and we can only place a lo wer limit of log N-e/cm(-3) greater than or equal to 7.8 to the electron de nsity in this object.