Potassium in the Galactic Bulge - as traced by microlensed dwarf & sub-giant stars

Sammanfattning: During this report the potassium (K) trend in the Galactic Bulge, with respect to metallicity and various α-elements, has been computed and evaluated by a method of line synthesis on the 7698.96 ̊A KI line (7699 KI), where Non-Local-Thermal-Equilibrium (NLTE) effects have been considered. Specifically, the α-elements of interest are calcium (Ca), titanium (Ti), silicon (Si), magnesium (Mg) and oxygen (O), due to the fact that these are believed to be valid tracer elements of Potassium due to their limited and/or well defined nucleosynthetic processes. The stellar sample used during the analysis is unique in the sense that it is the first sample of low- to intermediate- mass stars from the Galactic Bulge, making it possible to investigate age dependencies of the metallicity trends. It is found that, for mildly metal-poor to metal-rich stars, almost all metallicity trends in the bulge exhibit large dispersion compared to what is found in disk(s). It is thus deemed uncertain to evaluate any age dependence’s for any of the trends, the only slight exception being [K/O], where the dispersion is not as large as in the other trends, and a slight age dependence of increasing [K/O] as a function of decreasing age is observed. An investigation of why this dispersion occurs was performed, where it was found that the large majority of the dispersion was due a group of stars exhibiting a unpredictable spectral feature - the 7699 KI was blended with an unknown line of varying strength. Possible explanations of these unknown lines are hypothesized to be due to Diffuse Interstellar Bands (DIBs) or interstellar KI, both of which would yield similar anomalies found in the spectra of said group of stars. It is thus assumed that no firm conclusion about the dispersion of the K-trends observed in the bulge can be made, due to the unknown nature of the blended lines. However, it is deemed probable that these blended lines contribute to a overestimation of the K abundance, but further investigation of these spectral features is necessary before any firm conclusions can be made about the K-trend and/ or possible enrichment of K in the Galactic Bulge.