The Hamburg/ESO R-process enhanced star survey (HERES)

Hayek, Wolfgang; Wiesendahl, U.; Christlieb, N.; Eriksson, K.; Korn, A. J.; Barklem, P. S.; Hill, V.; Farouqi, K.; Pfeiffer, B.; Kratz, Karl

doi:10.1051/0004-6361/200811121

Cited by 87 publications

(116 citation statements)

References 72 publications

(93 reference statements)

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“…This rules out a low f odd . Our analysis is also in agreement with the results of Hayek et al (2009), who determined log (Ba) = −0.14. ii) Since the atmosphere of very metal-poor stars can be subject to deviation from LTE, we performed NLTE calculations, following the procedure of Mashonkina et al (1999).…”

Section: Neutron Capture Elementssupporting

confidence: 92%

“…i) We tested the exact same methodology on HE1219-0312, a well-known r-process enhanced star with [Eu/Fe] = +1.4 (Hayek et al 2009). Using the spectrum reduced by Norbert Christlieb, we find a mean abundance of the Ba  5853 Å, 6141 Å, and 6496 Å, lines to be log ε = −0.06 ± 0.03 in LTE calculation, and −0.16 ± 0.11 in NLTE.…”

Section: Neutron Capture Elementsmentioning

confidence: 99%

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The early days of the Sculptor dwarf spheroidal galaxy

Jablonka

North

Mashonkina

et al. 2015

A&A

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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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Section: Neutron Capture Elementssupporting

confidence: 92%

Section: Neutron Capture Elementsmentioning

confidence: 99%

The early days of the Sculptor dwarf spheroidal galaxy

Jablonka

North

Mashonkina

et al. 2015

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“…However, Th is further enhanced relative to this pattern in four stars: CS 31082-001, CS 30306-132 (Honda et al 2004), CS 31078-018 (Lai et al 2008) and HE 1219-0312 (Hayek et al 2009) -the so-called "actinide boost". In these stars, the actinides clearly had a different nucleosynthesis history than the stable third-peak elements.…”

Section: The R-element-rich Emp Stars and The Actinidesmentioning

confidence: 94%

First stars

Barbuy

Spite

Hill

et al. 2011

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Context. A small fraction of extremely metal-poor (EMP) stars exhibit moderate to extreme excesses of heavy neutron-capture elements produced in the r-process. The production site(s) of these elements in the early Galaxy remain(s) unclear, as is the reason for their occasional enhancement in the otherwise regular pattern of abundances of elements up to the iron peak. The detailed abundance pattern of the heaviest elements in EMP stars provides insight into their origin and role in the chemical enrichment of the early Galaxy and in radioactive nucleochronology. Aims. The EMP giant star CS 31082-001 ([Fe/H] ∼ −2.9) exhibits an extreme enhancement of neutron-capture elements ([r/Fe] ∼ +1.7) with U and Th enhanced by a further ∼+0.7 dex, and a minimum of blending by molecular lines such as CH or CN. A rich inventory of r-process element abundances was established previously from optical spectra. Here we aim to supplement these data with abundances from near-UV spectroscopy of the third-peak neutron-capture elements, which are crucial for understanding the synthesis of the heaviest elements. Methods. Near-UV spectra from HST/STIS were analysed with LTE model atmospheres and spectrum synthesis calculations to derive new abundances of Os, Ir, Pt, Au, Bi and Pb in CS 31082-001. Results. Together with earlier data, the resulting abundance pattern for the r-process elements provides improved constraints on the nature of the r-process. The observed U and Th abundances and the initial production ratio place CS 31082-001 as one of the oldest stars in the Galaxy, consistent with its extreme metal deficiency. Comparison with the heaviest stable reference elements and with the daughter nuclides Pb and Bi provides a consistency check on this age determination. Finally, the existence of such r-element rich stars indicate that the early chemical evolution of the Galaxy was localised and inhomogeneous.

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“…The actinide thorium is one such radioactive species. It is produced in the r-process, and has been widely used, particularly log (Th/Eu), for cosmochronometry to estimate stellar ages (e.g., Sneden et al 1996;Hill et al 2002;Honda et al 2004;Frebel et al 2007;Hayek et al 2009). Some authors have argued that log (Th/Eu) is not a reliable chronometer to derive stellar ages, because of the relatively large uncertainties (e.g., Goriely & Clerbaux 1999;Goriely & Arnould 2001;Honda et al 2004;Frebel et al 2007).…”

Section: Introductionmentioning

confidence: 99%

“…The HERES survey offers a good opportunity to perform such a study. More than 22 elemental abundances (not including Th) for the sample stars have been reported in previously published papers in this series (e.g., Barklem et al 2005;Zhang et al 2011), and thorium abundances have been studied furtherly with better quality spectra in a few stars (Hayek et al 2009;Mashonkina et al 2010). …”

Section: Introductionmentioning

confidence: 99%

The Hamburg/ESO R-process Enhanced Star survey (HERES)

Ren

Christlieb

Zhao

2012

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We report thorium abundances for 77 metal-poor stars in the metallicity range of −3.5 < [Fe/H] < −1.0, based on "snapshot" spectra obtained with VLT-UT2/UVES during the HERES Survey. We were able to determine the thorium abundances with better than 1σ confidence for 17 stars, while for 60 stars we derived upper limits. For five stars common with previous studies, our results were in good agreement with the literature results. The thorium abundances span a wide range of about 4.0 dex, and scatter exists in the distribution of log (Th/Eu) ratios for lower metallicity stars, supporting previous studies suggesting the r-process is not universal. We derived ages from the log (Th/Eu) ratios for 12 stars, resulting in large scattered ages, and two stars with significant enhancement of Th relative to Eu are found, indicating the "actinide boost" does not seem to be a rare phenomenon and thus highlighting the risk in using log (Th/Eu) to derive stellar ages.

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The Hamburg/ESO R-process enhanced star survey (HERES)

Cited by 87 publications

References 72 publications

The early days of the Sculptor dwarf spheroidal galaxy

The early days of the Sculptor dwarf spheroidal galaxy

First stars

The Hamburg/ESO R-process Enhanced Star survey (HERES)

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