Spectral Analysis of Neutron Capture Elements in the Laboratory and Stars

Sammanfattning: The pedigree of the elements heavier than iron is a vital question in the history and evolution of our galaxy. The elements up to and including those of the iron group are produced mainly through fusion processes within stars, giving the stars their energy. The even heavier elements are instead mainly produced through neutron capture processes: weak s-process, main s-process and r-process. The weak s-process is responsible for a portion of the nucleons up to about A=100 and is thought to be active mainly during helium-core burning in stars more massive than ~10 Msol. The main s-process and the r-process produce all heavier elements. The main s-process is active in AGB stars and the r-process is active in supernovae. This thesis deals with different aspects of neutron capture nucleosynthesis. Improved oscillator strengths and wavelengths for Hf II, Os I and Ir I have been determined and applied to the spectrum analysis of the metal-poor halo star CS31082-001, and the new abundances improve the abundance trend showing a pure r-process content of this star. Isotope shift in Sm II lines can be used to allow us to directly measure the r- vs s- process content in an object. This method is applied to CS31082-001, and it suggests that the star contains predominantly r-processed material. A search for evidence of weak s-process elements in alpha Orionis is also conducted and results show a strong enhancement of strontium.