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

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.

arXiv commentAccepted for publication in the Astrophysical Journal Supplement Series (32 pages, 4 figures, 4 tables)

References in corpus (12)

• The NumPy array: a structure for efficient numerical computation
• The s Process: Nuclear Physics, Stellar Models, Observations
• Origin of the Heaviest Elements: the Rapid Neutron-Capture Process
• A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
• The Abundances of Neutron Capture Species in the Very Metal-Poor Globular Cluster M15: An Uniform Analysis of RGB and RHB Stars
• Neutron Star Mergers Might not be the Only Source of r-Process Elements in the Milky Way
• The s-Process in Low Metallicity Stars. II. Interpretation of High-Resolution Spectroscopic Observations with AGB models
• New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars
• New Hubble Space Telescope Observations of Heavy Elements in Four Metal-Poor Stars
• The R-Process Alliance: A Comprehensive Abundance Analysis of HD 222925, a Metal-Poor Star with an Extreme R-Process Enhancement of [Eu/H] = -0.14
• Hubble Space Telescope Near-Ultraviolet Spectroscopy of Bright CEMP-s Stars
• Transition probabilities of Co II, weak lines to the ground and low metastable levels

Cited by in corpus (4)

• The R-Process Alliance: Abundance Universality among Some Elements at and between the First and Second R-Process Peaks
• Gaia-Sausage-Enceladus star formation history as revealed by detailed elemental abundances
• The R-Process Alliance: Hunting for gold in the near-UV spectrum of 2MASS J05383296-5904280
• The R-Process Alliance: A Nearly Complete R-Process Abundance Template Derived from Ultraviolet Spectroscopy of the R-Process-Enhanced Metal-Poor Star HD 222925