Hyperfine Structure and Isotope Shifts in Dy II

Dylan Del Papa, Richard Holt, S. Rosner
2017 Atoms  
Using fast-ion-beam laser-fluorescence spectroscopy (FIBLAS), we have measured the hyperfine structure (hfs) of 14 levels and an additional four transitions in Dy II and the isotope shifts (IS) of 12 transitions in the wavelength range of 422-460 nm. These are the first precision measurements of this kind in Dy II. Along with hfs and IS, new undocumented transitions were discovered within 3 GHz of the targeted transitions. These atomic data are essential for astrophysical studies of chemical
more » ... dies of chemical abundances, allowing correction for saturation and the effects of blended lines. Lanthanide abundances are important in diffusion modeling of stellar interiors, and in the mechanisms and history of nucleosynthesis in the universe. Hfs and IS also play an important role in the classification of energy levels, and provide a benchmark for theoretical atomic structure calculations. Atoms 2017, 5, 5 2 of 10 formed from the debris of the very first generation of initially metal-free massive stars (Population III). These studies shed light on the earliest nucleosynthesis of heavy elements in the universe and how they were incorporated into later stars [8,9]. CH stars, which are deficient in Fe and enhanced in C and s-process elements, obtained their heavy elements by mass transfer from now-unseen white dwarf binary companions when the latter were in the AGB stage of evolution. Thus the composition of CH stars reveals information about AGB synthesis of s-process elements [10]. Accurate abundance information is also required in the study of diffusion processes within stars, where chemical fractionation occurs due to a combination of gravity, convection and radiation pressure. The chemically peculiar (CP) stars exhibit typically large lanthanide abundance excesses relative to solar and meteoritic values, and the abundance pattern expected from nucleosynthesis may be greatly perturbed [4]. One of the most exciting recent developments in stellar astrophysics has been the rapid expansion of the field of asteroseismology [11], in which the observation of natural, resonant oscillations provides information about stellar interiors and evolution. These observations can be photometric or velocity measurements from Doppler shifts. In the latter case, it is essential to be able to model spectral line shapes accurately, requiring good atomic data. Extensive spectroscopy of Dy II has been done principally by Conway and Worden [12], Wyart [13][14][15], and more recently by Nave and Griesmann [16], who pointed out the complexity of lanthanide spectra due to the large number of terms arising from the unfilled 4f shell and the fact that 4f, 5d, and 6s electrons all have similar binding energies. The NIST Atomic Spectra Database [17] lists 576 levels of which a significant number are only partly classified as to principal configuration and term, and configuration mixing is common. One of the tools that has been used to aid in level classification is IS, since the 'field shift' part of the IS (the dominant contribution in heavy atoms) depends on the electron density at the nucleus and therefore is a function of the electronic states involved in a transition. Early measurements of IS were carried out by Pacheva and Abadjieva [18]. Aufmuth [19] measured IS for Dy isotopes 162-164 in 29 lines of Dy II in order to check the mixing of three configurations calculated by Wyart [13-15]. Ahmad et al. [20] measured the IS of 62 spectral lines, three of which overlap with our measurements. The only previous report of hfs is by Murakawa and Kamei [21].
doi:10.3390/atoms5010005 fatcat:w7n5wxz6cfcq7n7efxechdnzju