At NIST, we are continuing our critical evaluation and compilation work on atomic transition probabilities. We have focused our efforts on Na, Mg, Al, Si and S – for all stages of ionization – and on Fe I and Fe II. These species were already compiled quite some time ago at NIST, but much new work has been done which enlarges and improves the database, mostly by sophisticated calculations. Thus, the new compilations contain about 5-10 times more transitions than the earlier data volumes, and often the uncertainties are significantly smaller. In our evaluation procedure, we start by considering all published results. Applying certain general assessment criteria, we then narrow our considerations to the sources with the most accurate results. One final numerical value is presented for each line strength, and an accuracy is assigned. NIST compilations are intended to be sources of standard reference data, so that data with large uncertainties are not included.

Large sources of data for Na, Mg, Al, Si and S are the “Opacity Project” [1] and the recent MCHF results of Tachiev and Fischer [2]. The Opacity Project R-matrix computations, which generally span quantum numbers up to n = 10 and l = 4, were performed in LS coupling. In general, the accuracy of computed line strengths decreases as the spectra become more complex. The MCHF calculations remain quite accurate, though they only span levels up to n = 3 (recently, some n = 4 levels have been included for Mg).

For the spectra of Fe I and Fe II, we have mainly utilized recent experimental data obtained by a combination of accurate lifetime and emission branching-ratio measurements. These new compilations have been expanded to about 2400 lines for Fe I and 900 lines for Fe II. We shall present a number of graphical comparisons in support of our data selections.

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