Europium, Samarium, and Neodymium Isotopic Fractions in Metal‐Poor Stars

Roederer, Ian U.; Lawler, J. E.; Sneden, Christopher; Cowan, J. J.; Sobeck, Jennifer; Pilachowski, Catherine A.

doi:10.1063/1.2905533

Cited by 3 publications

(3 citation statements)

References 52 publications

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“…[Fe/H] is defined by the Fe abundance for the final set of T eff , log(g), and v t . We increase the overall metallicity Z of the atmosphere by +0.4 dex to account for the extra electrons from the α-elements that contribute to the H − continuous opacity; this artificial increase alters our derived abundances of the electrondonating elements by 0.01 dex and is completely negligible when elemental abundance ratios are considered (see, e.g., § 4.3 of Roederer et al 2008). We adopt the following atmospheric parameters for HKII 17435-00532: T eff / log(g)/v t /[Fe/H] = 5200 K/2.15/2.0 km s −1 /−2.23.…”

Section: Atmospheric Parametersmentioning

confidence: 99%

The Hobby-Eberly Telescope "Chemical Abundances of Stars in the Halo" (CASH) Project. I. The Lithium-, s-, and r-Enhanced Metal-Poor Giant HKII 17435-00532

Roederer,

Frebel,

Shetrone

et al. 2008

Preprint

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We present the first detailed abundance analysis of the metal-poor giant HKII 17435-00532. This star was observed as part of the University of Texas long-term project Chemical Abundances of Stars in the Halo (CASH ). A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope with a resolving power of R ∼ 15, 000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal-poor ([Fe/H] = −2.2) star has an unusually high lithium abundance (log ε (Li) = +2.1), mild carbon ([C/Fe] = +0.7) and sodium ([Na/Fe] = +0.6) enhancement, as well as enhancement of both s-process ([Ba/Fe] = +0.8) and r-process ([Eu/Fe] = +0.5) material. The high Li abundance can be explained by self-enrichment through extra mixing that connects the convective envelope with the outer regions of the H-burning shell. If so, HKII 17435-00532 is the most metal-poor star in which this short-lived phase of Li enrichment has been observed. The Na and n-capture enrichment can be explained by mass transfer from a companion that passed through the thermally-pulsing AGB phase of evolution with only a small initial enrichment of r-process material present in the birth cloud. Despite the current non-detection of radial velocity variations (over ∼ 180 days), it is possible that HKII 17435-00532 is in a long-period or highly-inclined binary system, similar to other stars with similar n-capture enrichment patterns.

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Section: Atmospheric Parametersmentioning

confidence: 99%

The Hobby-Eberly Telescope "Chemical Abundances of Stars in the Halo" (CASH) Project. I. The Lithium-, s-, and r-Enhanced Metal-Poor Giant HKII 17435-00532

Roederer,

Frebel,

Shetrone

et al. 2008

Preprint

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“…Observationally, the isotopic composition of neutron capture elements in galactic stars has been measured only for few elements (e.g., Ba, Sm, Nd and Eu) so far (Roederer et al 2008;Gallagher et al 2015), whereas the elemental abundances are available for much more elements (with the notable exception of In). The uncertainty ranges and primary key reactions for each es-process element are summarized in Table 8.…”

Section: Key Reactions In the Es-processmentioning

confidence: 99%

Uncertainties in s-process nucleosynthesis in massive stars determined by Monte Carlo variations

Nishimura

Hirschi

Rauscher

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The s-process in massive stars produces the weak component of the s-process (nuclei up to A ∼ 90), in amounts that match solar abundances. For heavier isotopes, such as barium, production through neutron capture is significantly enhanced in very metal-poor stars with fast rotation. However, detailed theoretical predictions for the resulting final s-process abundances have important uncertainties caused both by the underlying uncertainties in the nuclear physics (principally neutron capture reaction and β-decay rates) as well as by the stellar evolution modeling. In this work, we investigated the impact of nuclear-physics uncertainties relevant to the s-process in massive stars. Using a Monte-Carlo based approach, we performed extensive nuclear reaction network calculations that include newly evaluated upper and lower limits for the individual temperature dependent reaction rates. We found that most of the uncertainty in the final abundances is caused by uncertainties in the neutron capture rates, while β-decay rate uncertainties affect only a few nuclei near s-process branchings. The sprocess in rotating metal-poor stars shows quantitatively different uncertainties and key reactions, although the qualitative characteristics are similar. We confirmed that our results do not significantly change at different metallicities for fast rotating massive stars in the very low metallicity regime. We highlight which of the identified key reactions are realistic candidates for improved measurement by future experiments.

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“…quality and quantity of Sm isotopic fractions first investigated by [17,23]. The substantial growth of n-capture abundances in very metal-poor stars over the past couple of decades has illuminated the role of the r-process in early Galactic nucleosynthesis.…”

Section: Pos(nic Xi)074 R-process Starsmentioning

confidence: 99%

r-process enhanced metal-poor stars

Sneden¹,

Roederer²,

Cowan³

et al. 2011

Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI)

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In this review we summarize the current state of some aspects of observational studies of low metallicity stars that have been enriched with products of rapid-neutron-capture (r-process) nucleosynthesis events. Attention will be drawn to the element domains where there is little star-tostar variation in relative abundances (such as the rare earths), and those with substantial variations (the lightest neutron-capture elements and the very heavy radioactive elements Th and U). We highlight some new work bearing on our understanding of the limits of abundance distributions that can be produced in the r-process. Finally, comments will be made on the metallicity at which significant contributions from the s-process can be seen in Galactic halo stars. 11th Symposium on Nuclei in the Cosmos, NIC XI

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Europium, Samarium, and Neodymium Isotopic Fractions in Metal‐Poor Stars

Cited by 3 publications

References 52 publications

The Hobby-Eberly Telescope "Chemical Abundances of Stars in the Halo" (CASH) Project. I. The Lithium-, s-, and r-Enhanced Metal-Poor Giant HKII 17435-00532

The Hobby-Eberly Telescope "Chemical Abundances of Stars in the Halo" (CASH) Project. I. The Lithium-, s-, and r-Enhanced Metal-Poor Giant HKII 17435-00532

Uncertainties in s-process nucleosynthesis in massive stars determined by Monte Carlo variations

r-process enhanced metal-poor stars

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