The<i>s</i>‐Process in Metal‐Poor Stars: Abundances for 22 Neutron‐Capture Elements in CS 31062‐050

Johnson, Jennifer A.; Bolte, Michael

doi:10.1086/382147

Cited by 86 publications

(86 citation statements)

References 88 publications

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“…These scenarios are supported by the predictions of Bisterzo et al (2006) which satisfactorily reproduce the general features of CEMP-rs neutron-capture patterns by assuming in their model an initial high r-process enrichment before slow neutron capture begins. In contrast, Johnson & Bolte (2004) and Masseron (2006) do not find a satisfactory combination of r-and s-process that reproduce the neutron-capture element pattern in CEMP-rs stars, and call for a modified neutroncapture process. In addition, the large number of CEMP-rs stars observed at low metallicities casts doubt on the likelihood of two-phase scenarios.…”

Section: Introductionmentioning

confidence: 81%

“…Following this argument, Johnson & Bolte (2004) failed to reproduce in detail the extensive abundance pattern observed in the CEMP-rs star CS 31062-50 by adding an s-process pattern to an r-process pattern. Furthermore, Masseron (2006) demonstrated that the addition of Ba and Eu abundances as observed in CEMP-s stars (representing the contribution of a low-metallicity AGB star) to the Ba and Eu abundance as observed in rII stars (representing the contribution of a low-metallicity massive star) falls below the amount of Ba and Eu observed in CEMP-rs stars.…”

Section: The Possible Nature Of the Companions To Cemp-rs Starsmentioning

confidence: 99%

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A holistic approach to carbon-enhanced metal-poor stars

Masseron

Johnson²,

Plez

et al. 2010

A&A

238

462

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Context. Carbon-enhanced metal-poor (CEMP) stars are known to have properties that reflect the nucleosynthesis of the first lowand intermediate-mass stars, because most have been polluted by a now-extinct AGB star. Aims. By considering abundances in the various CEMP subclasses separately, we try to derive parameters (such as metallicity, mass, temperature, and neutron source) characterising AGB nucleosynthesis from the specific signatures imprinted on the abundances, and separate them from the impact of thermohaline mixing, first dredge-up, and dilution associated with the mass transfer from the companion. Methods. To place CEMP stars in a broader context, we collect abundances for about 180 stars of various metallicities (from solar to [Fe/H] = −4), luminosity classes (dwarfs and giants), and abundance patterns (e.g. C-rich and poor, Ba-rich and poor), from both our own sample and the literature. Results. We first show that there are CEMP stars that share the properties of CEMP-s stars and CEMP-no stars (which we refer to as CEMP-low-s stars). We also show that there is a strong correlation between Ba and C abundances in the s-only CEMP stars. This represents a strong detection of the operation of the 13 C neutron source in low-mass AGB stars. For the CEMP-rs stars (seemingly enriched with elements from both the s-and r-processes), the correlation of the N abundances with abundances of heavy elements from the 2nd and 3rd s-process peaks bears instead the signature of the 22 Ne neutron source. Since CEMP-rs stars also exhibit O and Mg enhancements, we conclude that extremely hot conditions prevailed during the thermal pulses of the contaminating AGB stars. We also note that abundances are not affected by the evolution of the CEMP-rs star itself (especially by the first dredge-up). This implies that mixing must have occurred while the star was on the main sequence, and that a large amount of matter must have been accreted so as to trigger thermohaline mixing. Finally, we argue that most CEMP-no stars (with neutron-capture element abundances comparable to non-CEMP stars) are likely the extremely metal-poor counterparts of CEMP neutron-capture-rich stars. We also show that the C enhancement in CEMP-no stars declines with metallicity at extremely low metallicity ([Fe/H] < −3.2). This trend is not predicted by any of the current AGB models.

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Section: Introductionmentioning

confidence: 81%

Section: The Possible Nature Of the Companions To Cemp-rs Starsmentioning

confidence: 99%

A holistic approach to carbon-enhanced metal-poor stars

Masseron

Johnson²,

Plez

et al. 2010

A&A

238

462

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“…The atomic lines were selected from previous abundance determinations of the heavy elements of stars, namely Sneden & Parthasarathy (1983), , Sneden et al (1996), Reddy et al (1997), Aoki et al (2001Aoki et al ( , 2002b, Cowan et al (2002), Sivarani et al (2004), and Johnson & Bolte (2004). The log gf values are primarily adopted from high-precision laboratory measurements; references are given in Table 2.…”

Section: Line Selection and Atomic Datamentioning

confidence: 99%

Abundances of neutron-capture elements in G 24-25

Liu

Nissen

Schuster

et al. 2012

A&A

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Aims. The differences between the neutron-capture element abundances of halo stars are important to our understanding of the nucleosynthesis of elements heavier than the iron group. We present a detailed abundance analysis of carbon and twelve neutron-capture elements from Sr up to Pb for a peculiar halo star G 24-25 with [Fe/H] = −1.4 in order to probe its origin. Methods. The equivalent widths of unblended lines are measured from high resolution NOT/FIES spectra and used to derive abundances based on Kurucz model atmospheres. In the case of CH, Pr, Eu, Gd, and Pb lines, the abundances are derived by fitting synthetic profiles to the observed spectra. Abundance analyses are performed both relative to the Sun and to a normal halo star G 16-20 that has similar stellar parameters as G 24-25. Results. We find that G 24-25 is a halo subgiant star with an unseen component. It has large overabundances of carbon and heavy s-process elements and mild overabundances of Eu and light s-process elements. This abundance distribution is consistent with that of a typical CH giant. The abundance pattern can be explained by mass transfer from a former asymptotic giant branch component, which is now a white dwarf.

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“…These examples suggest a significant contribution from the r-process to Eu. (An alternative possibility is a contribution of the s-process with a quite different condition, e.g., with very high neutron density; Johnson & Bolte 2004). However, the [Ba/Eu] of these objects is still much higher than that of the r-process-element-enhanced stars (½Ba/Eu $ À0:8; e.g., Sneden et al 1996Sneden et al , 2003.…”

Section: Sample Stars and Their Compositionsmentioning

confidence: 99%

The Origins of Two Classes of Carbon‐enhanced, Metal‐poor Stars

Ryan¹,

Aoki²,

Norris³

et al. 2005

ApJ

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We have compiled composition, luminosity, and binarity information for carbon-enhanced, metal-poor (CEMP) stars reported by recent studies. We divided the CEMP star sample into two classes having high and low abundances, respectively, of the s-process elements and consider the abundances of several isotopes, in particular, 12 C, 13 C, and 14 N, as well as the likely evolutionary stages of each star. Despite the fact that objects in both groups were selected from the same surveys (primarily the HK survey), without a priori knowledge of their s-process element abundances, we identify the following remarkable differences between the two classes: s-element-rich CEMP (CEMP-s) stars occupy a wide range of evolutionary states, but do not have a strongly evolved 13 C/ 14 N ratio, whereas s-elementnormal CEMP stars (CEMP-no) are found only high up the first-ascent giant branch and possess 13 C/ 14 N ratios approaching the CN cycle equilibrium value. We argue that these observational constraints can be accommodated by the following scenarios. CEMP-s stars acquire their distinctive surface compositions during their lifetimes when mass is transferred from an AGB companion that has recently synthesized 12 C and s-process elements. Such mass-accreting stars can be enriched at almost any stage of their evolution and hence are found throughout the H-R diagram. Dilution of transferred surface material as the accretor ascends the giant branch and its surface convective zone deepens may reduce the number of such stars, whose surfaces remain C-rich at high luminosities. Many, but not necessarily all, such stars should currently be in binary systems. Li-preserving CEMP-s stars may require a different explanation. In contrast, a CEMP-no star is proposed to have formed from gas that was enriched in 12 C from the triple-process in a previous generation of stars, some of which has been converted to 13 C and 14 N during the present star's giant branch evolution. The binary fraction of such stars should be the same as that of non-carbon-enhanced, metal-poor stars.

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Thes‐Process in Metal‐Poor Stars: Abundances for 22 Neutron‐Capture Elements in CS 31062‐050

Cited by 86 publications

References 88 publications

A holistic approach to carbon-enhanced metal-poor stars

A holistic approach to carbon-enhanced metal-poor stars

Abundances of neutron-capture elements in G 24-25

The Origins of Two Classes of Carbon‐enhanced, Metal‐poor Stars

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