Thomas Bensby
Senior lecturer
Observational Studies of the Chemical Evolution in the Galactic Thin and Thick Disks
Author
Summary, in English
The origin and evolution of the thin and thick disks in the Galaxy have been studied by means of detailed stellar abundances. High-resolution spectra of 102 F and G dwarf stars have been obtained with the spectrographs on the ESO 3.6-m and ESO 1.5-m telescopes on La Silla (Chile), the Very Large Telescope (VLT) on Paranal (Chile), and the Nordic Optical Telescope (NOT) on La Palma (Canary Islands, Spain). Abundances for 14 elements (O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, Ba, and Eu) have been determined. The following results were found: 1) Both the thin and the thick disks show distinct and well-defined abundance trends at sub-solar metallicities; 2) The thick disk shows signatures of chemical enrichment from Type Ia Supernovae; 3) [O/Fe] in the thin disk continues to decrease linearly at super-solar metallicities; 4) The abundance trends we see in the thick disk are invariant with distance from the Galactic plane ($Z_{
m max}$) and galactocentric radius ($R_{
m m}$); 4) The thick disk sample is in the mean older than the thin disk sample.
The thesis also includes an investigation of ages and metallicities in the thick disk. The results from this study are; 5) There is a possible age-metallicity relation present in the thick disk, 6) Star formation has been ongoing for several billion years in the thick disk.
Based on these findings, together with other constraints from the literature, we discuss different formation scenarios for the thick disk. We suggest that the currently most likely formation scenario is a violent merger event or a close encounter between the Galaxy and a companion galaxy.
m max}$) and galactocentric radius ($R_{
m m}$); 4) The thick disk sample is in the mean older than the thin disk sample.
The thesis also includes an investigation of ages and metallicities in the thick disk. The results from this study are; 5) There is a possible age-metallicity relation present in the thick disk, 6) Star formation has been ongoing for several billion years in the thick disk.
Based on these findings, together with other constraints from the literature, we discuss different formation scenarios for the thick disk. We suggest that the currently most likely formation scenario is a violent merger event or a close encounter between the Galaxy and a companion galaxy.
Department/s
- Lund Observatory - Has been reorganised
Publishing year
2004
Language
English
Full text
Document type
Dissertation
Publisher
Lund Observatory, Lund University
Topic
- Astronomy, Astrophysics and Cosmology
Keywords
- Astronomy
- Astronomi
- Fysicumarkivet A:2004:Bensby
Status
Published
Supervisor
- Sofia Feltzing
- Ingemar Lundström
ISBN/ISSN/Other
- ISBN: 91-628-5954-4
- LUNFD6/(NFAS 1028)/1-228/(2004)
Defence date
27 March 2004
Defence time
10:15
Defence place
Lundmarksalen, Institutionen för astronomi, Sölvegatan 27, Lund
Opponent
- Gerard Gilmore (Prof)