Lifetime measurements and oscillator strengths in singly ionized scandium and the solar abundance of scandium

Abstract

The lifetimes of 17 even-parity levels (3d5s, 3d4d, 3d6s and 4p2 ) in the region 57 743-77 837 cm −1 of singly ionized scandium (Sc II) were measured by two-step timeresolved laser induced fluorescence spectroscopy. Oscillator strengths of 57 lines from these highly excited upper levels were derived using a hollow cathode discharge lamp and a Fourier transform spectrometer. In addition, Hartree-Fock calculations where both the main relativistic and core-polarization effects were taken into account were carried out for both low-and high-excitation levels. There is a good agreement for most of the lines between our calculated branching fractions and the measurements of Lawler & Dakin in the region 9000-45 000 cm −1 for low excitation levels and with our measurements for high excitation levels in the region 23 500-63 100 cm −1 . This, in turn, allowed us to combine the calculated branching fractions with the available experimental lifetimes to determine semi-empirical oscillator strengths for a set of 380 E1 transitions in Sc II. These oscillator strengths include the weak lines that were used previously to derive the solar abundance of scandium. The solar abundance of scandium is now estimated to log = 3.04 ± 0.13 using these semi-empirical oscillator strengths to shift the values determined by Scott et al. The new estimated abundance value is in agreement with the meteoritic value (log met = 3.05 ± 0.02) of Lodders, Palme & Gail.

Atomic data for the Gaia-ESO Survey

“…These should be considered for laboratory measurements in the long term, but they are of lower immediate priority. Note that for the five Sc ii lines with gf_flag=N, new theoretical g f -values based on branching fractions calculated using the relativistic Hartree-Fock method and life-times measured by Marsden et al (1988) are available in Pehlivan Rhodin et al (2017a). Finally, there are a number of species with low-quality g f -values for 50% or more of the synflag=Y or U lines, which should be given highest priority in current and future laboratory experiments.…”

Evidence against Anomalous Compositions for Giants in the Galactic Nuclear Star Cluster

“…Compiled data for both the observed stars and stars used for comparisons in this paper. We assume solar abundances of A(Fe) = 7.45 (Grevesse et al 2007) and A(Sc) = 3.04 (Pehlivan Rhodin et al 2017 This is the case for most iron-group elements such as Fe I, where the lower excitation levels, such as the 4s levels, do not have near-IR transitions. For Sc I, the structure is different, with low-excitation transitions 3d 2 4s-3d4s4p appearing in the K-band.…”

The Laboratory Astrophysics Spectroscopy Programme at Imperial College London

“…Lifetimes can be measured with time-resolved laser-induced fluorescence (TRLIF) [28,29] or beam foil techniques [25], or obtained from theoretically calculated values. The main challenges of this method are the need to measure all the significant transitions coming from the upper energy level of interest (even if those spectral lines can lie very far apart in terms of wavelength) and the necessity of the upper energy level lifetime, which sets the absolute scale in this case (as the A ul does in the previous method).…”