A Search for Stars of Very Low Metal Abundance. Vi. Detailed Abundances of 313 Metal-Poor Stars

Roederer, Ian U.; Preston, George W.; Thompson, I. B.; Shectman, Stephen; Sneden, Christopher; Burley, Greg; Kelson, Daniel D.

doi:10.1088/0004-6256/147/6/136

Cited by 412 publications

(689 citation statements)

References 214 publications

(231 reference statements)

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“…It is important to emphasise that the [Sc/Fe] ratios of our stars are similar to those in outer MW halo stars (e.g., Gratton & Sneden 1991;McWilliam 1995;Roederer et al 2014). This is in stark contrast to the extremely low [Sc/Fe] ratios predicted for massive Population III SNe by, e.g., Nomoto et al (2006) and Heger & Woosley (2010), and to the recent observation of such depletions in bulge stars by Casey & Schlaufman (2015).…”

Section: Scandium: No Evidence For Population III Enrichmentsupporting

confidence: 56%

“…However, a NLTE analysis of Cr in metal-poor, warm dwarfs by Bergemann & Cescutti (2010), led them to conclude that the deficiencies found in LTE analyses could be explained by NLTE effects, rather than genuine deficiencies in [Cr/Fe]. This conclusion is supported by the lack of ionisation equilibrium obtained in this study: from our single Cr II line we find Cobolt in all stars is solar to moderately elevated, although we do not trace the slightly decreasing trend, towards higher metallicity, commencing at ∼−2 dex, seen in the Roederer et al (2014) [Co/Fe] for the one metal-poor giant in their sample with parameters similar to our stars. The maximum line-by-line deviation can even be higher, with corrections up to 0.9 dex for the case of the 4121 Å line that we also employed in our analysis.…”

Section: Scandium: No Evidence For Population III Enrichmentsupporting

confidence: 45%

“…1 were not corrected for NLTE; Andrievsky et al (2010) computed NLTE corrections of the order 0.2−0.4 dex (in the sense LTE−NLTE) for halo stars of similar stellar parameters, albeit at metallicities lower by ∼1 dex. Figure 1 indicates that our [Mg/Fe] is higher (by ∼0.15 dex) than the Roederer et al (2014) halo sample, at a mean of 0.51 dex and a low 1σ dispersion of 0.07 dex. It is also important to note that r-process rich bulge star from Johnson et al (2013) resembles our metal-poor bulge sample more than it does the halo stars.…”

Section: α-Elements: Mg Si Ca Timentioning

confidence: 81%

“…We also include the metal-poor bulge candidates of Howes et al (2014; filled blue squares) and Casey & Schlaufman (2015; open blue squares), the r-process enriched bulge star from Johnson et al (2013b;orange diamond), and blue points designate the bulge sample of Johnson et al (2012Johnson et al ( ,2014. Finally, black dots are halo stars from Roederer et al (2014), while black triangles are upper limits from that study. Note that their sample extended as metal-poor as [Fe/H] = −4.6 dex, but we truncated the axis for better readability.…”

Section: Scandium: No Evidence For Population III Enrichmentmentioning

confidence: 99%

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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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Section: Scandium: No Evidence For Population III Enrichmentsupporting

confidence: 56%

Section: Scandium: No Evidence For Population III Enrichmentsupporting

confidence: 45%

Section: α-Elements: Mg Si Ca Timentioning

confidence: 81%

Section: Scandium: No Evidence For Population III Enrichmentmentioning

confidence: 99%

See 2 more Smart Citations

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

Koch

McWilliam

Preston

et al. 2016

A&A

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“…40, 41, and references in refs. 42,43). We used spectrum synthesis to derive abundances of Ba, La, Pr, and Eu.…”

Section: Observations and Abundance Analysismentioning

confidence: 99%

R-process enrichment from a single event in an ancient dwarf galaxy

Frebel

Chiti

et al. 2016

Nature

388

489

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The elements heavier than zinc are synthesized through the (r)apid and (s)low neutroncapture processes 1,2 . The primary astrophysical production site of the r-process elements (such as europium) has been debated for nearly 60 years 2 . Chemical abundance trends of old Galactic halo stars initially suggested continual r-process production from sources like core-collapse supernovae 3,4 , but evidence in the local universe favored r-process production primarily from rare events like neutron star mergers 5,6 . The appearance of a europium abundance plateau in some dwarf spheroidal galaxies was suggested as evidence for rare rprocess enrichment in the early universe 7 , but only under the assumption of no gas accretion into the dwarf galaxies. Invoking cosmologically motivated gas accretion 8 actually favors continual r-process enrichment in those systems. Furthermore, the universal r-process pattern 1,9 has not been cleanly identified in dwarf spheroidals. The smaller, chemically simpler, and more ancient ultra-faint dwarf galaxies assembled shortly after the formation of the first stars and are ideal systems to study nucleosynthesis processes such as the r-process 10,11 . Reticulum II is a recently discovered ultra-faint dwarf galaxy [12][13][14] . Like other such galaxies, the abundances of non-neutron-capture elements are similar to those of other old stars 15 . Here we report that seven of nine stars in Reticulum II observed with high-resolution spectroscopy show strong enhancements in heavy neutroncapture elements with abundances that exactly follow the universal r-process pattern above barium. The enhancement in this "r-process galaxy" is 2-3 orders of magnitude higher than what is seen in any other ultra-faint dwarf galaxy 11,16,17 . This implies that a single rare event produced the r-process material in Reticulum II, whether or not gas accretion was significant in ultra-faint dwarf galaxies. The r-process yield and event rate is incompatible with ordinary core-collapse supernova 18 but consistent with other possible sites, such as neutron star mergers 19 .Ultra-faint dwarfs (UFDs) are small galaxies that orbit the Milky Way and have been discovered by deep wide-area sky surveys 12,13 . Although physically close to us, they are also relics from the era of the first stars and galaxies and thus an ideal place to investigate the first metal enrichment events in the universe 10 . Observations of UFDs provide evidence that they form all their stars within 1-3 Gyr of the Big Bang 20 , their stars contain very small amounts of elements heavier than helium ("metals") 21 , and they are enriched by the metal output of only a few generations of stars 11,20 . The chemical abundances of light elements (less heavy than iron) suggested that corecollapse supernovae were the primary metal sources in these systems 11,16,17 . This conclusion was supported by unusually low neutron-capture element abundances that are consistent with small amounts of neutron-capture element production associated with massive star evolution...

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On the chemical composition of the evolved very bright metal‐poor star HD 1936

Çalışkan,

Alazzawi,

Nasolo

2024

Astron Nachr

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We present chemical abundances of the very bright metal‐poor star HD 1936 based on high‐resolution and high SNR spectra from AUKR. We obtain the abundances of 29 atomic species with atomic numbers between 3 and 63. In this context, the derived lithium abundance of 1.01 is consistent with the thin Li plateau observed in lower red giant branch stars. The star is a carbon‐normal with a ratio of −0.31, just like other low‐luminosity red giants on the thin Li plateau. We find the ratios of [Eu/Fe] = 0.43 and [Ba/Eu] = −0.64, indicating very little s‐process contamination. These ratios allow us to classify the star as a moderately r‐process‐enhanced (r‐I) metal‐poor star for the first time. It is worth mentioning that the star has a metallicity of −1.74, a [Cu/Fe] of −0.74, a [Zn/Fe] of 0.04, and a [Mg/C] of 0.69. The results suggest that it may be a second‐generation star formed in a multi‐enriched environment, rather than being a descendant of very massive first‐generation stars. A last point worth mentioning is the possibility that HD 1936 may host a sub‐stellar component with a mass of . Although our study does not confirm or deny this, we briefly discuss the possibility of the star hosting a planet.

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A Search for Stars of Very Low Metal Abundance. Vi. Detailed Abundances of 313 Metal-Poor Stars

Cited by 412 publications

References 214 publications

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

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

R-process enrichment from a single event in an ancient dwarf galaxy

On the chemical composition of the evolved very bright metal‐poor star HD 1936

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