THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ –3.5, ,

Yong, David; Norris, John E.; Bessell, M. S.; Christlieb, N.; Asplund, Martin; Beers, Timothy C.; Barklem, P. S.; Frebel, Anna; Ryan, Sean G.

doi:10.1088/0004-637x/762/1/26

Cited by 295 publications

(266 citation 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: 92%

“…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%

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TOPoS

Bonifacio

Caffau

Spite

et al. 2015

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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: 92%

Section: On the Carbon Abundances In Cemp Starsmentioning

confidence: 99%

TOPoS

Bonifacio

Caffau

Spite

et al. 2015

A&A

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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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“…To obtain an improved estimate of the gravity, we used the Yale isochrones (Demarque et al 2004) and an IDL program by Yong et al (2013). However, the program failed to return a value for this very evolved RR Lyrae star.…”

Section: Stellar Parameters and Abundancesmentioning

confidence: 99%

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Hansen¹,

Rich

Koch

et al. 2016

A&A

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Low-mass variable high-velocity stars are interesting study cases for many aspects of Galactic structure and evolution. Until recently, the only known high-or hyper-velocity stars were young stars thought to originate from the Galactic center. Wide-area surveys such as APOGEE and BRAVA have found several low-mass stars in the bulge with Galactic rest-frame velocities higher than 350 km s −1 . In this study we present the first abundance analysis of a low-mass RR Lyrae star that is located close to the Galactic bulge, with a space motion of ∼-400 km s −1 . Using medium-resolution spectra, we derived abundances (including upper limits) of 11 elements. These allowed us to chemically tag the star and discuss its origin, although our derived abundances and metallicity, at [Fe/H] = −0.9 dex, do not point toward one unambiguous answer. Based on the chemical tagging, we cannot exclude that it originated in the bulge. However, its retrograde orbit and the derived abundances combined suggest that the star was accelerated from the outskirts of the inner (or even outer) halo during many-body interactions. Other possible origins include the bulge itself, or the star might have been stripped from a stellar cluster or the Sagittarius dwarf galaxy when it merged with the Milky Way.

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THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ –3.5, ,

Cited by 295 publications

References 137 publications

TOPoS

TOPoS

The early days of the Sculptor dwarf spheroidal galaxy

Chemical abundances in a high-velocity RR Lyrae star near the bulge

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