Atomic Influences in Stellar Spectroscopy

This thesis is a description of how knowledge of atomic physics can be used in a stellar spectrum analysis. Stellar investigations are spectroscopically performed based on wavelengths, intensities and spectral line structure. Properties such as isotopic shifts, hyperfine structure, Zeeman effect, line blending and spectral line broadening are investigated in stellar spectra to improve results of abundance investigation but also to extract additional information from the stellar spectrum about subjects such as stellar magnetic field strength and isotopic mixture in the stellar photosphere. Zeeman effect is investigated and a simple technique to measure stellar magnetic fields in Ap/Bp stars is developed. Hyperfine structure and isotope shifts are incorporated into a stellar spectrum analysis in an attempt to solve the gallium abundance ambiguity observed in HgMn stars. Isotopic shifts have also been observed in laboratory spectra of Sm III and oscillator strengths are derived for this ion based on lifetime and branching fraction measurements. Finally, the importance of line blending in stellar spectra is investigated, based on comparisons between observational data obtained with different spectral resolving powers.