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Abstract

Stars preserve the fossil records of the kinematical and chemical evolution of individual building blocks of the Milky Way. In its efforts to excavate this information, the astronomical community has recently seen the advent of massive astrometric and spectroscopic observing campaigns that are dedicated to gather extensive data for millions of stars. The exploration of these vast datasets is at the heart of the present thesis. First, I introduce ATHOS, a data-driven tool that employs spectral flux ratios for the determination of the fundamental stellar parameters effective temperature, surface gravity, and metallicity, upon which all higher-order parameters like detailed chemical abundances critically rely. ATHOS’ robustness and widespread applicability is not only showcased in a comparison to large-scale spectroscopic surveys and their dedicated pipelines, but it is also demonstrated to be able to compete with highly specialized parameterization methods that are tailored to high-quality data in the realm of studies with low target numbers. An in-depth study of the latter kind is outlined in the second part of this thesis, where I present a chemical abundance investigation of the metal-poor Galactic halo star HD 20. Using spectra and photometric time series of utmost quality in combination with modern asteroseismic and spectroscopic analysis techniques, I deduce a comprehensive, highly accurate, and precise chemical pattern that proves HD 20 worthy of being added to the short list of metal-poor benchmark stars, both for nuclear astrophysics and in terms of stellar parameters. The decomposition of the chemical pattern shows an imprint from s-process nucleosynthesis on top of the already in itself rarely encountered enhancement of r-process elements. In the absence of a companion that could act as polluter, this poses a striking finding that points towards fast and efficient mixing in the early interstellar medium prior to HD 20’s formation. In the third and last part, spectroscopic data from the SDSS/SEGUE surveys are combined with astrometry from the Gaia mission to form a sample of several hundred thousand chemodynamically characterized halo stars that is scrutinized to establish links between globular clusters and the general halo field star population. Based on the identified sample of probable cluster escapees that includes both first-generation and second-generation (former) cluster stars, I provide important observational constraints on the overall cluster contribution to the buildup of the Galactic halo. A highly interesting – yet tentative – finding is that for those populations of stars that were lost early on, the first-generation fraction appears higher compared to groups that are currently being stripped or still bound to clusters. This observation could indicate either a dominant contribution from since dissolved low-mass clusters or that early cluster mass loss preferentially affected first-generation stars.