J. A. Fedchak

Absolute UV and Vacuum UV Oscillator Strengths for Ni II

Radiative lifetimes, measured using time-resolved laser-induced fluorescence, are reported for 18 odd-parity levels of Ni+. The radiative lifetimes are combined with Ni II emission branching fractions to produce 59 accurate (typically ±10%) absolute atomic transition probabilities in the ultraviolet (UV) and vacuum ultraviolet (VUV). The UV and VUV branching fractions are determined using a combination of measurements from a Fourier transform spectrometer at the University of Lund and a 3 m focal length vacuum echelle spectrometer system at the University of Wisconsin. Accurate f-values for Ni II resonance lines are important for analysis of spectra on the diffuse interstellar medium (ISM) at low redshift and for studies of the same lines in high-redshift QSO absorption line systems. Resonance lines at vacuum wavelengths of 170.960, 174.155, and 175.191 nm have log gf values of -0.68, -0.60, and -0.80, respectively. Until additional laboratory measurements are completed, we recommend thatf-values for other Ni II resonance lines be taken from the relative f-values from Zsargo & Federman with a multiplicative scaling factor of 0.534 (±10%). The present measurements indicate that nickel is less depleted in the ISM than previously estimated.

Experimental and theoretical radiative lifetimes, branching fractions, and oscillator strengths for Lu I and experimental lifetimes for Lu II and Lu III

Radiative lifetimes, accurate in most cases to ±5%, from time-resolved, laser-induced fluorescence measurements on a slow beam of lutetium atoms and ions are reported for 22 odd-parity levels and 4 even-parity levels of Lu I and 14 odd-parity levels of Lu II. In addition, we report the radiative lifetime of one odd-parity level and an upper bound on the radiative lifetime of a second odd-parity level of Lu III. Experimental branching fractions for Lu I from emission spectra covering the near ultraviolet to the near infrared and recorded using the US National Solar Observatory 1.0 m Fourier transform spectrometer are reported. The branching fractions are combined with the radiative lifetimes to produce 44 experimentally determined transition probabilities or oscillator strengths, accurate generally to ±10%, for Lu I. New theoretical values for Lu I radiative lifetimes and branching fractions from a relativistic Hartree-Fock calculation that includes core polarization effects are also reported. These experimental and theoretical results, as well as older published results, are compared.

Vacuum Ultraviolet Resonance Absorption f-values for Ni II

We have used the High Sensitivity Absorption Spectroscopy experiment at the Synchrotron Radiation Center in Stoughton, Wisconsin, to measure relative absorption oscillator strengths, or f-values, for six resonance transitions of Ni+ in the vacuum ultraviolet. This laboratory absorption work is an extension of recent laser induced fluorescence and emission work which established an accurate, absolute scale for Ni II resonance f-values. The relative absorption f-values are normalized using three absolute f-values for Ni II, previously determined by combining experimental radiative lifetimes and emission branching fractions, to produce an expanded set of seven absolute resonance f-values for Ni II. Accurate f-values for Ni II resonance lines are critical to the analysis of spectra on the diffuse interstellar medium and are used to determine various properties of the ISM. Resonance lines of Ni II are also observed in high redshift QSO absorption line systems.

Absorption f-Values of Ti II Vacuum Ultraviolet Resonance Transitions

We report laboratory measurements of the oscillator strengths for the Ti II vacuum ultraviolet resonance transitions 3d24s a4F3/2-3d4s4p(3Po) 4F at λvac = 191.0938 nm and 3d24s a4F3/2-3d4s4p(3Po) 4D at 191.0609 nm. Using the High Sensitivity Absorption Spectroscopy Experiment at the Synchrotron Radiation Center in Stoughton, Wisconsin, we determined the f-values for the Ti II 191.06 and 191.09 nm transitions relative to the well-known f-values of the Ti II resonance transitions 3d24s a4F3/2-3d24p z4D at λvac = 306.7245 nm and 3d24s a4F3/2-3d24p z4G at 338.4740 nm. The Ti II 191.06 nm absorption f-value is 0.104 ± 0.004. The Ti II 191.09 nm absorption f-value is 0.098 ± 0.003. The Ti II 191.06 and Ti II 191.09 nm transitions have been detected in ground-based observations of high-redshift quasi-stellar object (QSO) absorption-line systems and in space-based observations. Use of these refined f-values causes a minimal change in the Ti abundances reported for some QSO absorption-line systems and for the Large Magellanic Cloud toward SN 1987A. The overabundance of Ti relative to Fe in comparison to solar abundances for two QSO absorption-line systems is decreased by our results. In general Ti abundances based on the 191 nm lines now can be put on an accurate absolute scale.

Radiative lifetimes of Tb ii

Radiative lifetimes measured by time-resolved laser-induced fluorescence are reported for 40 odd-parity levels and 36 even-parity levels of singly ionized terbium. The odd-parity levels range in energy from 29 000 to 40 000 cm-1 and those of even-parity from 21 000 to 37 000 cm-1. These lifetimes, with one exception, are accurate to ±5%. They will provide an absolute scale for accurate atomic-transition probabilities in Tb ii (the second spectrum of terbium).