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We report new branching fraction measurements for 199 UV and opticaltransitions of Hf II. These transitions range in wavelength (wavenumber) from2068- 6584 A (48322-15183 cm-1) and originate in 17 odd-parity upper levelsranging in energy from 38578-53227 cm-1. The branching fractions are combinedwith radiative lifetimes reported in an earlier study to produce a set oftransition probabilities and log(gf) values with accuracy ranging from 5-25%.Comparison is made to transition probabilities from the literature where suchdata exist. We use these new transition probabilities to derive improved Hfabundances in two metal-poor stars. HD 196944 is enhanced in s-processelements, and we derive log epsilon (Hf) = -0.72 +/- 0.03 (sigma = 0.09) from12 Hf II lines. HD 222925 is enhanced in r-process elements, and we derive logepsilon (Hf) = 0.32 +/- 0.03 (sigma = 0.11) from 20 Hf II lines. Thesemeasurements greatly expand the number of potentially useful Hf II lines foranalysis in UV and optical spectra.

Improved Atomic Transition Probabilities for UV and Optical Lines of Hf II and Determination of the Hf Abundance in Two Metal-Poor Stars