An observation study of metal poor stars of middle spectral type in the solar neighborhood

In this thesis study, carried out within the scope of TUBITAK 1001 project number 121F265, spectral, kinematic, orbital dynamics and age analyses were performed for the stars HD8724, HD63791 and HD195633 selected from the project stellar group. High resolution echelle spectra used for the determination of elemental abundances were obtained from the ELODIE spectral library. The astrometric data needed for kinematic calculations were obtained from GAIA DR3. Galactic population separations based on kinematics were tested with the α-element abundance ratios and Fe abundances determined for the thesis stars. The Python library is used for Galactic orbital parameters, and the Bayesian-based age determination method outlined in ¸Sahin and Bilir (2020) was used for age calculations. The chemical abundances obtained were evaluated together with galactic kinematics, dynamics and age data to assess the origin of the program stars in globular clusters in our Galaxy and satellite dwarf galaxies in the vicinity of our Galaxy. Main-sequence and red giant branch stars of intermediate spectral types (F and G spectral stars), which have main-sequence lifetimes comparable to the age of the galaxy, exhibit the chemical composition of the molecular cloud from which they formed. Therefore, the abundances of heavy elements detected in the atmospheres of these stars provide important information about the chemical evolutionary history of our Galaxy. In particular, the study of the spectral, kinematic and orbital dynamical properties of mid-spectral stars in the solar neighbourhood allows us to distinguish between different population groups in our Galaxy. Although the number of studies on metal-poor stars in the solar neighbourhood, where the spectral, kinematic and orbital dynamical properties of these stars are investigated together, is minimal, their number is increasing day by day thanks to the developing analysis techniques and survey programs. It is clear that the data, when the analysis methods applied to the project stars studied in this thesis are applied to a larger group of stars of statistical significance, will make a significant contribution to the literature on the chemical structures and dynamics of stars in the solar neighbourhood. As a matter of fact, the analysis techniques applied in this thesis will be repeated for 90 metal-poor (-2.5 < [Fe/H] (dex) < -0.5) sample stars of the G spectral type, which are targeted for analysis within the scope of the aforementioned TÜB˙ITAK 1001 project. In this sense, this thesis can be considered as a preliminary analysis phase for the project. In addition to their metal-poor characteristics, the high proper motion (μ > 100 mas/year) stars in the project star group constitute %66 of the total sample size. The stars HD63791 and HD195633, which were selected for the analysis in this thesis to represent the sample group, are high proper motion stars. HD63791 is also a metal-poor star, which was chosen to create a line list for the analysis of the ELODIE spectra of the whole project stars. Almost all the sources to be analysed in this thesis are stars that exhibit large differences in temperature, gravitational acceleration and metal abundances from those reported in the literature and were analyzed in such a comprehensive framework (spectroscopic, kinematic and dynamical methods) for the first time. To the best of our knowledge, there is no comprehensive study in the literature on metal-poor high-motion stars of spectral type G that examines the globular cluster or dwarf galaxy origins of these stars, using Bayesian ages, kinematic and Galactic orbital parameters, metal and α-element abundances together. In the future, the spectral, kinematic and orbital dynamics analysis methodology followed in this thesis will continue to be applied to other project stars. The spectral analyses carried out in a relatively limited spectral range with ELODIE spectra are planned to be extended to cover a wider wavelength range, especially for project stars whose data are listed in libraries providing high-resolution spectral data such as PolarBase. For this purpose, the line identification of the star HD218209, whose PolarBase echelle spectrum was obtained, have been partially completed (covering the wavelength range valid for the ELODIE spectral library). With the final line list, the wavelength limit for spectral analyses will be increased from 6800 Å to 10 000 Å.