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Abundances of disk and bulge giants from high-resolution optical spectra : IV. Zr, La, Ce, Eu

Forsberg, R. LU ; Jönsson, H. LU orcid ; Ryde, N. LU orcid and Matteucci, F. (2019) In Astronomy & Astrophysics 631.
Abstract
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 α-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... (More)
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 α-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 ~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] ~−0.4, pointing at similar enrichment to α-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. (Less)
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author
; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
stars: abundances, Galaxy: bulge, solar neighborhood, Galaxy: evolution
in
Astronomy & Astrophysics
volume
631
article number
A113
pages
15 pages
publisher
EDP Sciences
external identifiers
  • scopus:85082694785
ISSN
1432-0746
DOI
10.1051/0004-6361/201936343
project
Abundances of Neutron-Capture Elements in the Galactic Bulge and Disk from High-Resolution Spectra
language
English
LU publication?
yes
id
95123ba6-97a3-428a-aa90-9b40d6af0498
date added to LUP
2021-03-10 16:32:14
date last changed
2024-04-18 04:22:30
@article{95123ba6-97a3-428a-aa90-9b40d6af0498,
  abstract     = {{<i>Context</i>. 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 <i>α</i>-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.<br/><br/><i>Aims</i>. 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.<br/><br/><i>Methods</i>. 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.<br/><br/><i>Results</i>. We find flat Zr, La, and Ce trends in the bulge, with a ~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] ~−0.4, pointing at similar enrichment to <i>α</i>-elements in all populations.<br/><br/><i>Conclusions</i>. 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.}},
  author       = {{Forsberg, R. and Jönsson, H. and Ryde, N. and Matteucci, F.}},
  issn         = {{1432-0746}},
  keywords     = {{stars: abundances; Galaxy: bulge; solar neighborhood; Galaxy: evolution}},
  language     = {{eng}},
  publisher    = {{EDP Sciences}},
  series       = {{Astronomy & Astrophysics}},
  title        = {{Abundances of disk and bulge giants from high-resolution optical spectra : IV. Zr, La, Ce, Eu}},
  url          = {{http://dx.doi.org/10.1051/0004-6361/201936343}},
  doi          = {{10.1051/0004-6361/201936343}},
  volume       = {{631}},
  year         = {{2019}},
}