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

TL;DR

This study provides new, precise transition probabilities for Hf II lines in UV and optical spectra, enabling more accurate hafnium abundance measurements in metal-poor stars, which enhances understanding of stellar nucleosynthesis.

Contribution

The paper presents new branching fractions and transition probabilities for 199 Hf II lines, significantly improving the data available for stellar abundance analysis.

Findings

Derived Hf abundances in two metal-poor stars with improved accuracy.

Expanded the set of useful Hf II lines for spectroscopic analysis.

Compared new transition probabilities with existing literature, confirming their reliability.

Abstract

We report new branching fraction measurements for 199 UV and optical transitions of Hf II. These transitions range in wavelength (wavenumber) from 2068- 6584 A (48322-15183 cm-1) and originate in 17 odd-parity upper levels ranging in energy from 38578-53227 cm-1. The branching fractions are combined with radiative lifetimes reported in an earlier study to produce a set of transition probabilities and log(gf) values with accuracy ranging from 5-25%. Comparison is made to transition probabilities from the literature where such data exist. We use these new transition probabilities to derive improved Hf abundances in two metal-poor stars. HD 196944 is enhanced in s-process elements, and we derive log epsilon (Hf) = -0.72 +/- 0.03 (sigma = 0.09) from 12 Hf II lines. HD 222925 is enhanced in r-process elements, and we derive log epsilon (Hf) = 0.32 +/- 0.03 (sigma = 0.11) from 20 Hf II lines. These measurements greatly expand the number of potentially useful Hf II lines for analysis in UV and optical spectra.