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Improved Cr II log(gf) values and abundance determinations in the photospheres of the Sun and metal-poor star HD 84937

Published

Author(s)

James E. Lawler, Chris Sneden, Gillian Nave, E. A. Den Hartog, N Emrahoglu, John J. Cowan

Abstract

New emission branching fraction (BF) measurements for 183 lines of the second spectrum of chromium (Cr II) and new radiative lifetime measurements from laser induced fluorescence for eight levels of the z4F and z4D levels of ionized Cr are reported. The goals of this study are to check and expand earlier, but still modern, transition probability measurements in Cr II and reconcile Solar and stellar Cr abundance values based on Cr I and Cr II lines. A total of 18 spectra from three Fourier Transform Spectrometers supplemented with ultraviolet spectra from a high resolution echelle spectrometer are used in the BF measurements. Radiative lifetimes from this study and earlier published studies are used to convert the BFs to absolute transition probabilities. These new laboratory data are applied to determine the Cr abundance log ε in the Sun and metal-poor star HD 84937. The mean result in the Sun is = 5.624 ± 0.009 (one standard deviation σ = 0.049; 31 lines) compared to = 5.644 ± 0.006 (σ = 0.051, 85 lines) on a scale with the hydrogen abundance log ε(H) = 12. A Saha or ionization balance test on the photosphere of HD 84937 is also performed yielding = 3.417 ± 0.006 (σ = 0.050, 74 lines) and 0 eV) = 3.374 ± 0.011 (σ = 0.061, 32 lines) for this dwarf star. The resonance (E. P. = 0 eV) lines of Cr I yield a somewhat lower abundance value. We find a correlation of Cr (both neutrals and ions) with the iron- peak element Ti, suggesting an associated or related nucleosynthetic production. This marks the fourth, and heaviest iron-peak element (along with Ti, V and Sc) that appears to have a similar (or correlated) production history - none of the other iron-peak elements appear to be associated with Cr.
Citation
Astrophysical Journal

Keywords

atomic data, Sun: abundances, stars: abundances, stars: Population II, stars: individual (HD 84937)
Created January 20, 2017, Updated February 19, 2017