Abundances of disk and bulge giants from high-resolution optical spectra IV. Zr, La, Ce, Eu
2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 631, article id A113Article in journal (Refereed) Published
Abstract [en]
Context. Observations of the Galactic bulge suggest that the disk formed through secular evolution rather than gas dissipation and/or mergers, as previously believed. This would imply very similar chemistry in the disk and bulge. Some elements, such as the alpha-elements, are well studied in the bulge, but others like the neutron-capture elements are much less well explored. Stellar mass and metallicity are factors that affect the neutron-capture process. Due to this, the enrichment of the ISM and the abundance of neutron-capture elements vary with time, making them suitable probes for Galactic chemical evolution. Aims. In this work, we make a differential comparison of neutron-capture element abundances determined in the local disk(s) and the bulge, focusing on minimising possible systematic effects in the analysis, with the aim of finding possible differences/similarities between the populations. Methods. Abundances are determined for Zr, La, Ce, and Eu in 45 bulge giants and 291 local disk giants, from high-resolution optical spectra. The abundances are determined by fitting synthetic spectra using the SME-code. The disk sample is separated into thin- and thick-disk components using a combination of abundances and kinematics. Results. We find flat Zr, La, and Ce trends in the bulge, with a similar to 0.1 dex higher La abundance compared with the disk, possibly indicating a higher s-process contribution for La in the bulge. [Eu/Fe] decreases with increasing [Fe/H], with a plateau at around [Fe/H] similar to -0.4, pointing at similar enrichment to alpha-elements in all populations. Conclusions. We find that the r-process dominated the neutron-capture production at early times both in the disks and bulge. Further, [La/Eu] ratios for the bulge are systematically higher than for the thick disk, pointing to either a) a different amount of SN II or b) a different contribution of the s-process in the two populations. Considering [(La+Ce)/Zr], the bulge and the thick disk follow each other closely, suggesting a similar ratio of high-to-low-mass asymptotic giant branch stars.
Place, publisher, year, edition, pages
EDP Sciences, 2019. Vol. 631, article id A113
Keywords [en]
stars: abundances, Galaxy: bulge, solar neighborhood, Galaxy: evolution
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:mau:diva-18679DOI: 10.1051/0004-6361/201936343ISI: 000507288200002Scopus ID: 2-s2.0-85082694785OAI: oai:DiVA.org:mau-18679DiVA, id: diva2:1477046
2020-10-162020-10-162024-01-22Bibliographically approved