Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy

Koch, Andreas and Feltzing, S. and Adén, D. and Matteucci, F. (2013) Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy. Astronomy and Astrophysics, 554. ISSN 1432-0746

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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 Å 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 ε(Ba)  ≲  0.7 dex (3σ). We discuss various possible systematic biasses, first and foremost, a blend with the Fe I 6141.73 Å-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.

Item Type:
Journal Article
Journal or Publication Title:
Astronomy and Astrophysics
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/1900/1912
Subjects:
ID Code:
83336
Deposited By:
Deposited On:
01 Dec 2016 11:16
Refereed?:
Yes
Published?:
Published
Last Modified:
19 Aug 2020 03:28