CHEMISTRY OF THE SAGITTARIUS DWARF GALAXY: A TOP-LIGHT INITIAL MASS FUNCTION, OUTFLOWS, AND THE<i>R</i>-PROCESS

McWilliam, Andrew; Wallerstein, George; Mottini, M.

doi:10.1088/0004-637x/778/2/149

Cited by 181 publications

(287 citation statements)

References 147 publications

(367 reference statements)

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“…Moreover, the correlation is quite similar to the correlation of field halo stars found by Frebel (2010). The current data soundly support previous results obtained by Carretta et al (2010b) and McWilliam et al (2013) for Sagittarius stars. The key advantage of the current comparison is that we investigate the correlation for a system that is significantly more metal-poor than Sagittarius (∼−2.0 vs. ∼−0.6 dex).…”

Section: Carina Chemical Enrichmentsupporting

confidence: 92%

“…This is the most metal-rich system and has Na abundances (purple asterisks) that are systematically lower by ∼0.3-0.5 dex than field halo stars and the few metal-rich stars in Sculptor (cyan triangles). A similar underabundance in Na was also found by McWilliam et al (2013) in RGs of the metal-rich Sagittarius dSph galaxy. This is a metallicity regime in which Na abundances might be affected by non-LTE effects (Gratton et al 1999;Carretta et al 2010b), but the detailed spectroscopic analysis performed by Fulbright et al (2007) among K-type giants and FGK-type dwarfs in the Galactic disk indicates that the non-LTE effects are weak (see also McWilliam et al 2013).…”

Section: Comparison With Nearby Dwarfssupporting

confidence: 80%

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The Carina Project

Fabrizio

Nonino

Bono

et al. 2015

A&A

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We have performed a new abundance analysis of Carina red giant (RG) stars from spectroscopic data collected with UVES (high spectral resolution) and FLAMES/GIRAFFE (high and medium resolution) at ESO/VLT. The former sample includes 44 RGs, while the latter consists of 65 (high-resolution) and ∼800 (medium-resolution) RGs, covering a significant fraction of the galaxy's RG branch, and red clump stars. To improve the abundance analysis at the faint magnitude limit, the FLAMES/GIRAFFE data were divided into ten surface gravity and effective temperature bins. The spectra of the stars belonging to the same gravity and temperature bin were stacked. This approach allowed us to increase the signal-to-noise ratio in the faint magnitude limit (V ≥ 20.5 mag) by at least a factor of five. We took advantage of the new photometry index c U,B,I introduced recently as an age and probably a metallicity indicator to split stars along the red giant branch. These two stellar populations display distinct [Fe/H] and [Mg/H] distributions: their mean iron abundances are −2.15 ± 0.06 dex (σ = 0.28), and −1.75 ± 0.03 dex (σ = 0.21), respectively. The two iron distributions differ at the 75% level. This supports preliminary results. Moreover, we found that the old and intermediate-age stellar populations have mean [Mg/H] abundances of −1.91 ± 0.05 dex (σ = 0.22) and −1.35 ± 0.03 dex (σ = 0.22); these differ at the 83% level. Carina's α-element abundances agree, within 1σ, with similar abundances for field halo stars and for cluster (Galactic and Magellanic) stars. The same outcome applies to nearby dwarf spheroidals and ultra-faint dwarf galaxies in the iron range covered by Carina stars. Finally, we found evidence of a clear correlation between Na and O abundances, thus suggesting that Carina's chemical enrichment history is quite different from that in the globular clusters.

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Section: Carina Chemical Enrichmentsupporting

confidence: 92%

Section: Comparison With Nearby Dwarfssupporting

confidence: 80%

The Carina Project

Fabrizio

Nonino

Bono

et al. 2015

A&A

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“…Such a chemical signature is rather dramatic at higher metallicity (Cohen 2004;Sbordone et al 2007), but it becomes more and more difficult to discern as metallicity decreases, since Sgr dSph chemical evolution at low metallicities appears to closely match the values observed in the MW halo (e.g. McWilliam et al 2013). We will now look in greater detail at some chemical markers that might be used to infer an association of NGC 5053 and NGC 5634 with Sgr dSph.…”

Section: Assessing the Proposed Association With Sgr Dsphmentioning

confidence: 97%

Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf spheroidal galaxy?

Sbordone

Monaco

Bidin

et al. 2015

A&A

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Context. The tidal disruption of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, it is suspected that the Sgr dSph has lost a number of globular clusters (GC). Many Galactic GC are thought to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed owing to chemical similarities, others exist whose chemical composition has never been investigated. Aims. NGC 5053 and NGC 5634 are two of these scarcely studied Sgr dSph candidate-member clusters. To characterize their composition we analyzed one giant star in NGC 5053, and two in NGC 5634. Methods. We analyze high-resolution and signal-to-noise spectra by means of the MyGIsFOS code, determining atmospheric parameters and abundances for up to 21 species between O and Eu. The abundances are compared with those of MW halo field stars, of unassociated MW halo globulars, and of the metal-poor Sgr dSph main body population.Results. We derive a metallicity of [Fe /H] = −2.26 ± 0.10 for NGC 5053, and of [Fe /H] = −1.99 ± 0.075 and −1.97 ± 0.076 for the two stars in NGC 5634. This makes NGC 5053 one of the most metal-poor globular clusters in the MW. Both clusters display an α enhancement similar to the one of the halo at comparable metallicity. The two stars in NGC 5634 clearly display the Na-O anticorrelation widespread among MW globulars. Most other abundances are in good agreement with standard MW halo trends. Conclusions. The chemistry of the Sgr dSph main body populations is similar to that of the halo at low metallicity. It is thus difficult to discriminate between an origin of NGC 5053 and NGC 5634 in the Sgr dSph, and one in the MW. However, the abundances of these clusters do appear closer to that of Sgr dSph than of the halo, favoring an origin in the Sgr dSph system.

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“…If 37860 was indeed a member of the metal-poor Sgr population, its regular abundance pattern points towards a chemical evolution of those parts that were stripped early on in the accretion process that was typical for similarly old, metal-poor environments (e.g., Roederer et al 2014;, contrasting the complex evolution of Sgr's compact and intact main body (McWilliam et al 2013), at higher [Fe/H].…”

Section: Star 37860 and Sagittariusmentioning

confidence: 99%

Metal-poor stars towards the Galactic bulge: A population potpourri

Koch

McWilliam

Preston

et al. 2016

A&A

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We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the southern edge of the Galactic bulge, at (l, b) ∼ (0 • ,−11 • ). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H] = −2.52 dex, and another target is a moderately metal-poor ([Fe/H] = −1.53 dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe] = 1.35). These individuals provide the first contenders of these classes of stars towards the bulge. Four of the carbon-normal stars exhibit abundance patterns reminiscent of halo star across a metallicity range spanning −2.0 to −2.6 dex, i.e., enhanced α-elements and solar Fe-peak and neutron-capture elements, and the remaining one is a regular metal-rich bulge giant. The position, distance, and radial velocity of one of the metal-poor HB stars coincides with simulations of the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their highly uncertain proper motions prohibit a clear kinematic separation, the stars' chemical abundances and distances suggest that these metal-poor candidates, albeit located towards the bulge, are not of the bulge, but rather inner halo stars on orbits that make them pass through the central regions. Thus, we caution similar claims of detections of metal-poor stars as true habitants of the bulge.

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CHEMISTRY OF THE SAGITTARIUS DWARF GALAXY: A TOP-LIGHT INITIAL MASS FUNCTION, OUTFLOWS, AND THER-PROCESS

Abstract: From chemical abundance analysis of stars in the Sagittarius dwarf spheroidal galaxy (Sgr), we conclude that the α-element deficiencies cannot be due to the Type Ia supernova (SN Ia) time-delay scenario of Tinsley. Instead, the evidence points to low [α/Fe]

Cited by 181 publications

References 147 publications

The Carina Project

The Carina Project

Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf spheroidal galaxy?

Metal-poor stars towards the Galactic bulge: A population potpourri

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