title: Determination of hyperfine-induced transition rates from observations of a planetary nebula.
abstract: Observations of the planetary nebula NGC3918 made with the STIS instrument on the Hubble Space Telescope reveal the first unambiguous detection of a hyperfine-induced transition 2s2p 3P(o)(0)-->2s2 1S0 in the berylliumlike emission line spectrum of N IV at 1487.89 A. A nebular model allows us to confirm a transition rate of 4x10(-4) sec(-1)+/-33% for this line. The measurement represents the first independent confirmation of the transition rate of hyperfine-induced lines in low ionization stages, and it provides support for the techniques used to compute these transitions for the determination of very low densities and isotope ratios.
authors.affiliation: Department of Physics, Lund University, Box 118, S-221 00 Lund, Sweden.
authors.forename: Tomas
authors.initials: T
authors.lastname: Brage
authors.forename: Philip G
authors.initials: PG
authors.lastname: Judge
authors.forename: Charles R
authors.initials: CR
authors.lastname: Proffitt