Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy

• Verfasst von: Koch-Hansen, Andreas [VerfasserIn]
• Verfasst von: Feltzing, Sofia [VerfasserIn]
• Verfasst von: Adén, D. [VerfasserIn]
• Verfasst von: Matteucci, F. [VerfasserIn]
• Titel: Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy
• Verf.angabe: A. Koch, S. Feltzing, D. Adén, and F. Matteucci
• E-Jahr: 2013
• Jahr: 28 May 2013
• Umfang: 10 S.
• Fussnoten: Gesehen am 07.06.2022
• Titel Quelle: Enthalten in: Astronomy and astrophysics
• Ort Quelle: Les Ulis : EDP Sciences, 1969
• Jahr Quelle: 2013
• Band/Heft Quelle: 554(2013), Artikel-ID A5, Seite 1-10
• ISSN Quelle: 1432-0746
• DOI: doi:10.1051/0004-6361/201220742
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1752020383

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 <i>ε<i/>(Ba) ≲ 0.7 dex (3<i>σ<i/>). 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.