Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy

Дата и время публикации : 2013-04-09T20:00:00Z

Авторы публикации и институты :
Andreas Koch
Sofia Feltzing
Daniel Aden
Francesca Matteucci

Ссылка на журнал-издание: Ссылка на журнал-издание не найдена
Коментарии к cтатье: 10 pages, 6 figures, accepted for publication in Astronomy & Astrophysics
Первичная категория: astro-ph.GA

Все категории : astro-ph.GA

Краткий обзор статьи: 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 AA 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) < 0.7 dex (3 sigma). We discuss various possible systematic biasses, first and foremost, a blend with the Fe I 6141.73 AA-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.

Category: Physics