The nature of stars with a common origin: clues from metallicity, elemental abundances, and kinematics

University dissertation from Department of Astronomy and Theoretical Physics, Lund University

Abstract: Most of field stars originate from dissolved star clusters. If the gas cloud is well mixed the stars in the cluster are expected to be chemically homogenous. Although the original kinematical information of a star may be lost under the Galactic dynamic evolution, the chemical signatures are preserved in the form of elemental abundances in individual low-mass stars. The present-day distribution of its stars therefore provides a strong constrain on the formation and evolution of the Galactic disks. The aim of this thesis is to search for the origins of group of stars with similar kinematics making use of their chemical signatures. To efficiently and accurately measure stellar parameters and elemental abundances from high-resolution spectra of dwarfs and subgiants, an improved methodology is developed. A modified chemical tagging method suited to our special case is used to group stars which could share the same birthplace. We firstly employ this method to look for the lost siblings of the Sun. Star HIP 40317 that has very similar abundance pattern to the Sun is likely a solar sibling. However, it is not directly supported by our dynamical arguments. Then, we also explore the possible origins of a newly discovered stellar stream. We exclude a dissolved star cluster as the progenitor of the KFR08 steam based on the results of chemical tagging experiment. The old and alpha-enhanced members of the stream have relatively hot kinematics. This suggests that the KFR08 stream originated from the thick disk population, which was perturbed by a massive merger in the early Universe. NGC 6528 is the most metal-rich globular cluster in bulge. It is an ideal local template that can be used to infer the properties of old and metal-rich populations. We develop a new method to accurately measure physical parameters and metallicity for a large sample of red giant brach stars. Radial velocity of the stars is used to select the cluster members. The metallicity distribution and elemental abundance analysis of NGC 6528 members suggest that the cluster experienced chemical enrichment dominated by SNe II, while having smaller contributions from both SNe Ia and intermediate-mass AGB stars.