Copper abundances of F and G dwarf stars in the Milky Way

University essay from Lunds universitet/Astronomi

Abstract: An investigation has been done in order increase the understanding of the origin and chemical evolution of copper in the Milky Way stellar disks. This is interesting to know as it plays a part of the Galaxy puzzle, so we become more able to map how and why galaxies look like they do. The atmosphere of a star keeps information about how elemental abundant the Universe was at the time and place of creation, as the atmosphere remains intact during its lifetime. Dwarf stars with their long lifetime of billions of years may in other word keep information about the early days of our Universe. So, by determining the copper abundances for 502 F and G dwarf stars in the Solar neighborhood of different age, the evolution of copper can be determined. The copper abundance was measured through comparisons of synthetic spectra, with different copper abundances, to observed spectra, where the spectrum with the best fit was chosen. The star sample was a compound of different observations. Mainly, the stars were chosen to trace and characterize the thin and thick disks in the Solar neighborhood. The stars were observed with the MIKE spectrograph on the Magellan Clay telescope. 491 out of these 502 stars were able to give results good enough to be taken into account. When the result was normalized to the Sun, it was found out that the copper abundance, of this star sample, ranges between -0.6 < [Cu/Fe] < 0.2 dex, while the metallicity for the star sample ranges between -1.7 < [Fe/H] < 0.4 dex. A rising copper abundance trend is seen in the metallicity range -1.7 < [Fe/H] < -0.6 dex, with a flat area between -0.6 < [Fe/H] < 0 dex. For [Fe/H] > 0 a rising trend is once again seen. This rising trend for the copper abundance supports the idea that copper comes from both type II supernovae, and that the contribution of copper is metallicity dependent. The flat trend supports the idea that copper is made in type Ia supernovae.

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