Hyperfine structure measurements in scandium for IR spectroscopy

Detta är en Master-uppsats från Lunds universitet/Astronomi; Lunds universitet/Institutionen för astronomi och teoretisk fysik

Sammanfattning: Stellar abundances are important for understanding the chemical evolution of galaxies and provide us with constraints on stellar evolution and supernova nucleosynthesis. To determine stellar abundances accurately, atomic data is crucial. This data is incomplete for many elements, especially in the infrared region. In particular, hyperfine structure (hfs) data in the near-infrared region is lacking for neutral scandium. Incorrect scandium abundances are obtained when hfs is neglected in stellar abundance analysis, which has led to contradicting theories of the synthesis process of scandium. In this project, hfs constants for neutral scandium are derived by means of laboratory experiments. A spectrum was produced using a hollow cathode discharge lamp and the spectrum was recorded using a Fourier Transform Spectrometer. A model has been developed to produce synthetic spectra of hfs multiplets. Using the nonlinear least squares method, the model was fitted to observed transitions in order to find the best fit hfs constants. The hfs constants have been determined for 95 levels in neutral scandium. For 52 of these levels, the hfs constants were determined for the first time. An agreement with literature values was found. The behaviour of the developed program was probed given an offset in initial values, and various signal to noise ratios and widths of the structure. Additionally, oscillator strengths have been derived for 590 hfs transitions, using the Höln-Kronig intensity rule. The hfs data derived in this project will allow for more accurate analysis of scandium lines in stellar spectra. The transition in scandium from $3d4s(^3D)4p$ $^4D_{{7}/{2}}$ to $3d^2(^3F)4s$ $^4F_{7/2}$ in the spectrum of the star Alpha Boötis has been investigated in the light of the new hfs data and the new hfs constants were able to reproduce the observed line profile.

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