A few years ago we published a small set of Fe II f-values of lines of astrophysical interest (Heise & Kock 1990) giving a solar iron abundance of log N(Fe) = 7.48 0.09 (Holweger et al., 1990). Later Hannaford et al.(1992) measured the corresponding lifetimes anew which they combined with our branching ratios. They obtained a solar abundance of log N(Fe) = 7.48 0.04, in agreement with our result. On the other hand the high Oxford value of Blackwell et al. (1984) derived from Fe I lines, log N(Fe) = 7.67 0.03, is still under discussion. A contribution in solving this puzzle could be better lifetime measurements, especially, by reducing systematic error sources.
We developed an improved apparatus to measure lifetimes below 5 ns more accurately with the time-resolved laser-induced fluorescence (TRLIF) technique. The improvement includes a short laser pulse, a linear ion trap, a faster photodetector and a more sophisticated evaluation procedure. The apparatus has successfully been tested on W II and is now used to measure a selected number of Fe II levels. We present the results together with our rescaled f-values, and also a new abundance determination is given.
© European Southern Observatory (ESO) 1999
Online publication: February 22, 1999