Measurement of relative oscillator strengths for Fe I: transitions from levels b3Fsub(2-4)(2.61 eV-2.56 eV). Use of a multipass optical system

The design of a three-pass optical system for use with the Oxford spectroscopic furnace is described. Relative oscillator strengths of 16 lines of Fe I (2.56 eV < chi < 2.61 eV, -0.9 > log gf > -2.7) measured by its use are presented. The accuracy of the relative values for the stronger lines is 0.006 dex (1.4 per cent) but some of the weaker lines have an accuracy of only 0.03 dex (7 per cent) because of possible blending. The relative values have been placed on an absolute scale through a comparison with Fe I 371.99 via Fe I lines of excitation energy 1.5 eV. Comparisons are made with the data of other experimenters and with theoretical values. A formula is proposed for adjusting the experimental results of Bridges and Kornblith (1974 Astrophys. J., 192, 793) to bring them into better agreement with the Oxford results. (author)