Detailed chemical abundances of neutron-capture elements - from 523 local giant stars

Detta är en Master-uppsats från Lunds universitet/Astronomi

Sammanfattning: Purpose: The purpose of this work is to determine the abundances of neutron-capture elements in solar neighborhood giant stars. This enables constraints to be put on the the cosmic origin of these elements. I have determined abundances of elements produced in both the weak s-process (Cu), the first and second s-process peaks (Y, Zr and La, Ce, Pr, Nd, respectively) and the r-process (Eu, Gd). The weak s-process is predicted to take place in the interior of massive stars, whereas the main s-process takes place in low-mass AGB stars. There are still several possibilities for production sites of the r-process. Comparing the abundances of these elements for a range of stellar metallicities can increase the understanding of their production sites and give clues to the evolution of the Galaxy. Method: The stellar sample consists of 523 giant stars in the local disk, all observed with the optical high-resolution spectrograph FIES at the Nordic Optical Telescope, on La Palma. The abundance determination is done by synthesising line profiles and comparing them to observed data. The use of giant stars in this work prepares for further and deeper probing of the Galaxy and its components. In addition, I can minimise the possible systematic uncertainties that comes with analysing giant stars. The stellar sample is divided into separate stellar populations, primarily based on chemistry and secondarily on kinematics. Results: The abundances determined are of high accuracy and compare well with previous work done on dwarf stars. This high quality allows outliers in the data to be found in addition to tracing the disk populations. In general I find that the thin disk is enriched in s-process-dominated elements, whilst the thick disk is enriched in r-process-dominated elements. The time delay of AGB stars becomes very clear in my results as well as allowing for detailed investigation of the first and second s-process peaks. I also note that the r-process-dominated elements have similar features as that of α-elements. Conclusions: With careful spectral analysis, detailed abundance determination of giant stars is possible, allowing measurements of distant stars at high resolution to be made. This is important for constraining models of the Galactic evolution and permits accurate abundance determinations of the neutron-capture elements.

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