NORMAL AND OUTLYING POPULATIONS OF THE MILKY WAY STELLAR HALO AT [Fe/H] &lt;–2

Cohen, Judith G.; Christlieb, N.; Thompson, I. B.; McWilliam, Andrew; Shectman, Stephen; Reimers, D.; Wisotzki, L.; Kirby, Evan N.

doi:10.1088/0004-637x/778/1/56

Cited by 190 publications

(216 citation statements)

References 131 publications

(210 reference statements)

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“…This implies that NLTE and granulation effects have opposite directions, and they may tend to cancel; however, for iron it is not possible to simply add the 3D Thompson et al 2008;Aoki et al 2008;Behara et al 2010;Placco et al 2011;Carollo et al 2012;Masseron et al 2010Masseron et al , 2012Yong et al 2013;Cohen et al 2013;Spite et al 2013;Caffau et al 2013a). The bimodal distribution is clear in this plot.…”

Section: Effects Of Granulationmentioning

confidence: 93%

“…6 we have included only unevolved stars since giant stars may be internally "mixed" (Spite et al 2005(Spite et al , 2006 and the C abundance may thus be decreased by an amount that is generally difficult to estimate. We have included in the plot only stars from the literature that have a measured Ba abundance or a significant upper limit (Sivarani et al 2006;Frebel et al 2005Frebel et al , 2006Thompson et al 2008;Aoki et al 2008;Behara et al 2010;Masseron et al 2010Masseron et al , 2012Yong et al 2013;Cohen et al 2013;Li et al 2015), so as to have some indication on their classification as CEMP-no, CEMP-s, or CEMP-rs. In order to clearly define the behaviour of the carbon abundance at low metallicity, we have also included the ultra-iron-poor subgiant HE 1327-2326 (Frebel et al 2005Cohen et al 2013) and SDSS J1619+1705 (Caffau et al 2013a), even though their Ba abundance is undetermined.…”

Section: On the Carbon Abundances In Cemp Starsmentioning

confidence: 99%

See 1 more Smart Citation

TOPoS

Bonifacio

Caffau

Spite

et al. 2015

A&A

174

232

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Context. In the course of the Turn Off Primordial Stars (TOPoS) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars. Aims. We want to provide the most complete chemical inventory for these six stars in order to constrain the nucleosynthesis processes responsible for the abundance patterns. Methods. We analyse both X-Shooter and UVES spectra acquired at the VLT. We used a traditional abundance analysis based on OSMARCS 1D local thermodynamic equilibrium (LTE) model atmospheres and the turbospectrum line formation code. were not able to detect any iron lines, yet we could place a robust (3σ) upper limit of [Fe/H] < −5.0 and measure the Ca abundance, with [Ca/H] = −5.0, and carbon, A(C) = 6.90, suggesting that this star could be even more metal-poor than SDSS J1742+2531. This makes these two stars the seventh and eighth stars known so far with [Fe/H] < −4.5, usually termed ultra-iron-poor (UIP) stars. No lithium is detected in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which implies a robust upper limit of A(Li) < 1.8 for both stars. Conclusions. Our measured carbon abundances confirm the bimodal distribution of carbon in CEMP stars, identifying a high-carbon band and a low-carbon band. We propose an interpretation of this bimodality according to which the stars on the high-carbon band are the result of mass transfer from an AGB companion, while the stars on the low-carbon band are genuine fossil records of a gas Article published by EDP Sciences A28, page 1 of 20 A&A 579, A28 (2015) cloud that has also been enriched by a faint supernova (SN) providing carbon and the lighter elements. The abundance pattern of the UIP stars shows a large star-to-star scatter in the [X/Ca] ratios for all elements up to aluminium (up to 1 dex), but this scatter drops for heavier elements and is at most of the order of a factor of two. We propose that this can be explained if these stars are formed from gas that has been chemically enriched by several SNe, that produce the roughly constant [X/Ca] ratios for the heavier elements, and in some cases the gas has also been polluted by the ejecta of a faint SN that contributes the lighter elements in variable amounts. The absence of lithium in four of the five known unevolved UIP stars can be explained by a dominant role of fragmentation in the formation of these stars. This would result either in a destruction of lithium in the pre-main-sequence phase, through rotational mixing or to a lack of late accretion from a reservoir of fresh gas. The phenomenon should have varying degrees of efficiency.

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Section: Effects Of Granulationmentioning

confidence: 93%

Section: On the Carbon Abundances In Cemp Starsmentioning

confidence: 99%

TOPoS

Bonifacio

Caffau

Spite

et al. 2015

A&A

174

232

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“…In all figures, the grey points show the location of RGB stars in the Milky Way halo (Honda et al 2004;Cayrel et al 2004;Spite et al 2005Spite et al , 2006Aoki et al 2005Aoki et al , 2007Cohen et al 2013Cohen et al , 2006Cohen et al , 2004Lai et al 2008;Yong et al 2013;Ishigaki et al 2013). The Sculptor stars are shown in orange.…”

Section: Comparison Samples: References Symbols and Colour Codes Inmentioning

confidence: 99%

The early days of the Sculptor dwarf spheroidal galaxy

Jablonka

North

Mashonkina

et al. 2015

A&A

165

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We present the high-resolution spectroscopic study of five −3.9 ≤ [Fe/H] ≤ −2.5 stars in the Local Group dwarf spheroidal, Sculptor, thereby doubling the number of stars with comparable observations in this metallicity range. We carry out a detailed analysis of the chemical abundances of α, iron peak, and light and heavy elements, and draw comparisons with the Milky Way halo and the ultra-faint dwarf stellar populations. We show that the bulk of the Sculptor metal-poor stars follow the same trends in abundance ratios versus metallicity as the Milky Way stars. This suggests similar early conditions of star formation and a high degree of homogeneity of the interstellar medium. We find an outlier to this main regime, which seems to miss the products of the most massive of the Type II supernovae. In addition to its help in refining galaxy formation models, this star provides clues to the production of cobalt and zinc. Two of our sample stars have low odd-to-even barium isotope abundance ratios, suggestive of a fair proportion of s-process. We discuss the implication for the nucleosynthetic origin of the neutron capture elements.

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“…These CEMP-s stars are HE 0206-1916 (Aoki et al 2007), HE 1045+0226 (Cohen et al 2013), HE 2330-0555 (Aoki et al 2007) and CS 10301-015 (Aoki et al 2002a,b). Non-rotating models cannot explain the considered CEMP-s stars.…”

Section: Comparison To Single Cemp-s Starsmentioning

confidence: 99%

Are some CEMP-s stars the daughters of spinstars?

Choplin

Hirschi

Meynet

et al. 2017

A&A

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Carbon-enhanced metal-poor (CEMP)-s stars are long-lived low-mass stars with a very low iron content as well as overabundances of carbon and s-elements. Their peculiar chemical pattern is often explained by pollution from an asymptotic giant branch (AGB) star companion. Recent observations have shown that most CEMP-s stars are in binary systems, providing support to the AGB companion scenario. A few CEMP-s stars, however, appear to be single. We inspect four apparently single CEMP-s stars and discuss the possibility that they formed from the ejecta of a previous-generation massive star, referred to as the "source" star. In order to investigate this scenario, we computed low-metallicity massive-star models with and without rotation and including complete s-process nucleosynthesis. We find that non-rotating source stars cannot explain the observed abundance of any of the four CEMP-s stars. Three out of the four CEMP-s stars can be explained by a 25 M source star with v ini ∼ 500 km s −1 (spinstar). The fourth CEMP-s star has a high Pb abundance that cannot be explained by any of the models we computed. Since spinstars and AGB predict different ranges of [O/Fe] and [ls/hs], these ratios could be an interesting way to further test these two scenarios.

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NORMAL AND OUTLYING POPULATIONS OF THE MILKY WAY STELLAR HALO AT [Fe/H] <–2

Cited by 190 publications

References 131 publications

TOPoS

TOPoS

The early days of the Sculptor dwarf spheroidal galaxy

Are some CEMP-s stars the daughters of spinstars?

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