Hyperfine structure in singly-ionized lutetium

Stellar abundance determinations require high quality atomic data to yield reliable results. In addition to accurate transition probabilities, hyperfine structure (HFS) and/or isotope shifts (IS) are also needed for spectral syntheses for some species. Lu⁺, which has substantial HFS, is one such species. Although generally not resolved at photospheric temperatures, HFS/IS must be incorporated to accurately desaturate a strong transition. In this study we have used the high-resolution University of Wisconsin 3-meter focal length echelle spectrograph to record spectra of a commercial Lu-Ne hollow cathode lamp operating at 20 mA. These spectra have yielded hyperfine patterns for 35 UV and blue transitions of Lu II. These patterns have been analyzed using a non-linear least-squares fitting routine to determine hyperfine structure constants for 16 levels of Lu⁺, of which 10 are being reported for the first time. The relatively low lamp current results in optically thin spectra in which both weak and strong HFS components match their theoretical relative component strength, making the fitting process much more robust and reliable. In this poster we will compare the use of the 3-m echelle spectrograph in this study to earlier work which used spectra from a 1-m Fourier transform spectrometer (FTS). Dispersive spectrometers, including the 3-m echelle, are free from the multiplex noise of interferometric spectrometers and thus many more lines are observable compared to the few observed previously using a FTS. This work is supported by NSF grant AST1814512 (E.D.H. and J.E.L) and NASA grants NNX16AE96G, HST-GO-15657.004-A (J.E.L.) and HST-GO-14765.001-A (I.U.R.).