The origin and chemical evolution of iron-peak and neutron-capture elements in the Milky Way disk
Author
Summary, in English
All the elements heavier than Li are created during stellar evolution. Even if our knowledge of this process is good, many questions still remain. For instance, the odd-Z iron-peak elements Sc, V, Mn, and Co together with neutron-capture elements Sr, Zr, La, Ce, Nd, Sm, and Eu have still unclear production sites because theoretical models and observational evidences are not in agreement. Having a clear picture of how, when, and where the different elements formed is important because elements with known origins can be used to study the chemical evolution of stellar populations and improve our knowledge on how our Galaxy and its stellar population formed and evolved.
The aim of this thesis is to try to improve the understanding of the production and evolution of these elements. The analysis was performed using a large sample of high-resolution spectra of dwarf stars in the solar neighbourhood, to probe the different populations of the Milky Way, with particular interest to the Galactic thin and thick disks.
Our results indicate that Sc, V, and Co are produced in Type II supernovae. In particular Co abundances seem to point to high production of Co in very massive stars in the early stage of the Galaxy. As soon as Type Ia supernovae start to enrich the interstellar medium with Fe, the abundance trends decrease to reach solar values. On the other hand Mn is produced in core collapse supernovae in the early stages of the Galaxy, but appears later to be produced in higher quantities in Type Ia supernovae. Neutron-capture elements are produced in a mix of two different processes, depending on the intensity of the neutron flux that happen in different sites and at different timescales in the Galactic evolution. Our results are generally in agreement with the recent theoretical calculation on how much and where these elements are produced. The same production sites can be inferred for Sr and Zr, for La and Ce, and for Nd and Sm. Finally, the different abundance trends at different stellar ages seems to indicate a change in the production sites between the transition from thick disk to thin disk for Sr, Zr, Nd, Sm, and Eu.
The aim of this thesis is to try to improve the understanding of the production and evolution of these elements. The analysis was performed using a large sample of high-resolution spectra of dwarf stars in the solar neighbourhood, to probe the different populations of the Milky Way, with particular interest to the Galactic thin and thick disks.
Our results indicate that Sc, V, and Co are produced in Type II supernovae. In particular Co abundances seem to point to high production of Co in very massive stars in the early stage of the Galaxy. As soon as Type Ia supernovae start to enrich the interstellar medium with Fe, the abundance trends decrease to reach solar values. On the other hand Mn is produced in core collapse supernovae in the early stages of the Galaxy, but appears later to be produced in higher quantities in Type Ia supernovae. Neutron-capture elements are produced in a mix of two different processes, depending on the intensity of the neutron flux that happen in different sites and at different timescales in the Galactic evolution. Our results are generally in agreement with the recent theoretical calculation on how much and where these elements are produced. The same production sites can be inferred for Sr and Zr, for La and Ce, and for Nd and Sm. Finally, the different abundance trends at different stellar ages seems to indicate a change in the production sites between the transition from thick disk to thin disk for Sr, Zr, Nd, Sm, and Eu.
Department/s
Publishing year
2015
Language
English
Document type
Dissertation
Publisher
Department of Astronomy and Theoretical Physics, Lund University
Topic
- Astronomy, Astrophysics and Cosmology
Keywords
- Stars: abundances
- Stars: solar-type
- Galaxy: disk
- Galaxy: evolution
- Galaxy: solar neighbourhood
Status
Published
Supervisor
ISBN/ISSN/Other
- ISBN: 978-91-7623-293-4
Defence date
5 June 2015
Defence time
09:00
Defence place
Lundmark lecture hall (Lundmarksalen), Deparment of Astronomy and Theoretical Physics
Opponent
- Sofia Randich