Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy
(2013) In Astronomy & Astrophysics 554.- Abstract
- We present an assessment of the barium abundance ratios for red giant member stars in the faint Hercules dwarf spheroidal (dSph) galaxy. Our results are drawn from intermediate-resolution FLAMES/GIRAFFE spectra around the Ba II 6141.71 angstrom absorption line at low signal-to-noise ratios. For three brighter stars we were able to gain estimates from direct equivalent-width measurements, while for the remaining eight stars only upper limits could be obtained. These results are investigated in a statistical manner and indicate very low Ba abundances of log epsilon(Ba) less than or similar to 0.7 dex (3 sigma). We discuss various possible systematic biasses, first and foremost, a blend with the Fe I 6141.73 angstrom-line, but most of those... (More)
- We present an assessment of the barium abundance ratios for red giant member stars in the faint Hercules dwarf spheroidal (dSph) galaxy. Our results are drawn from intermediate-resolution FLAMES/GIRAFFE spectra around the Ba II 6141.71 angstrom absorption line at low signal-to-noise ratios. For three brighter stars we were able to gain estimates from direct equivalent-width measurements, while for the remaining eight stars only upper limits could be obtained. These results are investigated in a statistical manner and indicate very low Ba abundances of log epsilon(Ba) less than or similar to 0.7 dex (3 sigma). We discuss various possible systematic biasses, first and foremost, a blend with the Fe I 6141.73 angstrom-line, but most of those would only lead to even lower abundances. A better match with metal-poor halo and dSph stars can only be reached by including a large uncertainty in the continuum placement. This contrasts with the high dispersions in iron and calcium (in excess of 1 dex) in this galaxy. While the latter spreads are typical of the very low luminosity, dark-matter dominated dSphs, a high level of depletion in heavy elements suggests that chemical enrichment in Hercules was governed by very massive stars, coupled with a very low star formation efficiency. While very low abundances of some heavy elements are also found in individual stars of other dwarf galaxies, this is the first time that a very low Ba abundance is found within an entire dSph over a broad metallicity range. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/3979130
- author
- Koch, A. ; Feltzing, Sofia LU ; Adén, Daniel LU and Matteucci, F.
- organization
- publishing date
- 2013
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- galaxies: evolution, abundances, nucleosynthesis, nuclear reactions, stars: abundances, stars: Population II, galaxies: dwarf, galaxies: individual: Hercules
- in
- Astronomy & Astrophysics
- volume
- 554
- article number
- A5
- publisher
- EDP Sciences
- external identifiers
-
- wos:000320444200005
- scopus:84878310426
- ISSN
- 0004-6361
- DOI
- 10.1051/0004-6361/201220742
- language
- English
- LU publication?
- yes
- id
- 524d2da5-bb2f-473e-a5e8-dd490e7aefba (old id 3979130)
- date added to LUP
- 2016-04-01 14:32:52
- date last changed
- 2024-03-27 18:30:56
@article{524d2da5-bb2f-473e-a5e8-dd490e7aefba, abstract = {{We present an assessment of the barium abundance ratios for red giant member stars in the faint Hercules dwarf spheroidal (dSph) galaxy. Our results are drawn from intermediate-resolution FLAMES/GIRAFFE spectra around the Ba II 6141.71 angstrom absorption line at low signal-to-noise ratios. For three brighter stars we were able to gain estimates from direct equivalent-width measurements, while for the remaining eight stars only upper limits could be obtained. These results are investigated in a statistical manner and indicate very low Ba abundances of log epsilon(Ba) less than or similar to 0.7 dex (3 sigma). We discuss various possible systematic biasses, first and foremost, a blend with the Fe I 6141.73 angstrom-line, but most of those would only lead to even lower abundances. A better match with metal-poor halo and dSph stars can only be reached by including a large uncertainty in the continuum placement. This contrasts with the high dispersions in iron and calcium (in excess of 1 dex) in this galaxy. While the latter spreads are typical of the very low luminosity, dark-matter dominated dSphs, a high level of depletion in heavy elements suggests that chemical enrichment in Hercules was governed by very massive stars, coupled with a very low star formation efficiency. While very low abundances of some heavy elements are also found in individual stars of other dwarf galaxies, this is the first time that a very low Ba abundance is found within an entire dSph over a broad metallicity range.}}, author = {{Koch, A. and Feltzing, Sofia and Adén, Daniel and Matteucci, F.}}, issn = {{0004-6361}}, keywords = {{galaxies: evolution; abundances; nucleosynthesis; nuclear reactions; stars: abundances; stars: Population II; galaxies: dwarf; galaxies: individual: Hercules}}, language = {{eng}}, publisher = {{EDP Sciences}}, series = {{Astronomy & Astrophysics}}, title = {{Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy}}, url = {{http://dx.doi.org/10.1051/0004-6361/201220742}}, doi = {{10.1051/0004-6361/201220742}}, volume = {{554}}, year = {{2013}}, }