eprintid: 28676
rev_number: 18
eprint_status: archive
userid: 5300
dir: disk0/00/02/86/76
datestamp: 2020-07-28 12:54:06
lastmod: 2020-08-06 12:33:40
status_changed: 2020-07-28 12:54:06
type: doctoralThesis
metadata_visibility: show
creators_name: Hanke, Michael
title: Probing the early Milky Way with stellar spectroscopy
subjects: ddc-520
divisions: i-130001
adv_faculty: af-13
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.
date: 2020
id_scheme: DOI
id_number: 10.11588/heidok.00028676
ppn_swb: 1726518027
own_urn: urn:nbn:de:bsz:16-heidok-286761
date_accepted: 2020-07-17
advisor: HASH(0x55fc36c975c8)
language: eng
bibsort: HANKEMICHAPROBINGTHE2020
full_text_status: public
place_of_pub: Heidelberg
citation:   Hanke, Michael  (2020) Probing the early Milky Way with stellar spectroscopy.  [Dissertation]     
document_url: https://archiv.ub.uni-heidelberg.de/volltextserver/28676/1/Thesis_Hanke.pdf