Subaru/HDS Abundances in Three Giant Stars in the Ursa Minor Dwarf Spheroidal Galaxy

Sadakane, Kozo; Arimoto, N.; Ikuta, Chisato; Aoki, Wako; Jablonka, P.; Tajitsu, Akito

doi:10.1093/pasj/56.6.1041

Cited by 98 publications

(141 citation statements)

References 36 publications

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“…These measurements show a general trend of lower [α/Fe] ratios at a given [Fe/H] than what is found in Galactic halo stars of comparable metallicity (e.g., Shetrone et al 2001;Fulbright 2002;Tolstoy et al 2003;Sadakane et al 2004;Geisler et al 2005;Monaco et al 2005;Sbordone et al 2007, Koch et al 2007d. Moreover, there is a lack of extremely metal-poor stars in all dSphs studied in detail so far, i.e., very few stars more metal-poor than [Fe/H] = −2.5 dex have been found (Helmi et al 2006;Koch et al 2007a).…”

Section: Detailed Chemical Abundancessupporting

confidence: 53%

Baryonic Properties of the Darkest Galaxies

Grebel¹

2007

Proc. IAU

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Abstract. The faintest and darkest galaxies that we know of today are the dwarf spheroidal (dSph) galaxies. They appear to be plausible counterparts of cosmologically predicted small subhalos though their numbers do not (yet?) suffice to resolve the substructure crisis. Their mass-to-light ratios may go up to 1000 for the faintest objects, and their total masses are of the order of a few 10 6 to 10 7 M . Though most dSphs are dominated by old populations, they all show extended and presumably slow star formation histories with considerable enrichment. While environment has certainly affected their evolution, as evidenced by the morphology-gasdistance relations, intrinsic properties such as their (initial) baryon content may also have played a major role. The complexity and diversity of their star formation histories is surprising, and there are no obvious evolutionary connections to dwarf irregulars.

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Section: Detailed Chemical Abundancessupporting

confidence: 53%

Baryonic Properties of the Darkest Galaxies

Grebel¹

2007

Proc. IAU

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“…Studies of abundances in individual stars in dwarf galaxies do not often report stars with light-element abundances similar to secondgeneration globular cluster stars. In Shetrone et al (2003) there is only one star out of the 15 surveyed (Fornax 21) with even mildly elevated [Na/Fe], Sadakane et al (2004) found fairly low [Na/Fe] abundances in the three stars they observed in Ursa Minor, and Geisler et al (2005) find the same result for nine RGB stars in Sculptor. Koch et al (2008) also report one star in Carina (of eight with measured sodium abundance) with moderate [Na/Fe], and Letarte et al (2010) report one star in Fornax (of 70 with measured sodium abundances) with moderate [Na/Fe], but neither study finds any stars with the level of sodium abundance enhancement typically found in second-generation globular cluster stars (e.g., Carretta et al 2009).…”

Section: Stellar Distancesmentioning

confidence: 68%

Building the Galactic halo from globular clusters: evidence from chemically unusual red giants

Martell

Smolinski

Beers

et al. 2011

A&A

161

193

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We present a spectroscopic search for halo field stars that originally formed in globular clusters. Using moderate-resolution SDSS-III/SEGUE-2 spectra of 561 red giants with typical halo metallicities (−1.8 ≤ [Fe/H] ≤ −1.0), we identify 16 stars, 3% of the sample, with CN and CH bandstrength behavior indicating depleted carbon and enhanced nitrogen abundances relative to the rest of the data set. Since globular clusters are the only environment known in which stars form with this pattern of atypical light-element abundances, we claim that these stars are second-generation globular cluster stars that have been lost to the halo field via normal cluster massloss processes. Extrapolating from theoretical models of two-generation globular cluster formation, this result suggests that globular clusters contributed significant numbers of stars to the construction of the Galactic halo: we calculate that a minimum of 17% of the present-day mass of the stellar halo was originally formed in globular clusters. The ratio of CN-strong to CN-normal stars drops with Galactocentric distance, suggesting that the inner-halo population may be the primary repository of these stars.

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“…also include, for comparison, Galactic stars from the compilation of Venn et al (2004;and references therein) and Milky Way dSph satellites including the more luminous dSphs (Shetrone et al 2001(Shetrone et al , 2003(Shetrone et al , 2009Fulbright et al 2004;Sadakane et al 2004;Geisler et al 2005;Aoki et al 2009;Cohen & Huang 2009;Frebel et al 2010a;Letarte et al 2010;Tafelmeyer et al 2010;Lemasle et al 2012;Venn et al 2012;and Starkenburg et al 2012) and the most recent measurements in a few ultrafaint dSphs (K08; Feltzing et al 2009;Frebel et al 2010b;Norris et al 2010b;Simon et al 2010;and Gilmore et al 2013). The Ba abundances and limits are very low, at a mean [Ba/H] of −3.97 from the three EW measurements, and [Ba/H] < −3.84 (2σ), <−3.55 (3σ), respectively.…”

Section: Resultsmentioning

confidence: 99%

Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy

Koch

Feltzing

Adén

et al. 2013

A&A

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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.

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Subaru/HDS Abundances in Three Giant Stars in the Ursa Minor Dwarf Spheroidal Galaxy

Cited by 98 publications

References 36 publications

Baryonic Properties of the Darkest Galaxies

Baryonic Properties of the Darkest Galaxies

Building the Galactic halo from globular clusters: evidence from chemically unusual red giants

Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy

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