Binarity among CEMP-no stars: an indication of multiple formation pathways?

Arentsen, Anke; Starkenburg, Else; Shetrone, Matthew; Venn, Kim A.; Depagne, É.; McConnachie, Alan W.

doi:10.1051/0004-6361/201834146

Cited by 74 publications

(63 citation statements)

References 100 publications

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“…Their estimated binary periods fall in the same range as CEMP-s stars, which is consistent with the expectation that the Group II and Group III stars belong to long period binaries. Indeed, one of the Group III stars, HE 0107-5240, was reported to have a companion star whose binary period is longer than 10000 days (Arentsen et al 2019). We also note that some CEMP-no stars also show Eu/Ba ratio predicted by the s-process nucleosynthesis, and that the distribution of [Ba/Fe] of CEMP-no stars is different from that of C-normal EMP stars (Yamada et al 2019b).…”

Section: Introductionmentioning

confidence: 52%

Are Faint Supernovae Responsible for Carbon-enhanced Metal-poor Stars?

Komiya

Suda

Yamada

et al. 2020

ApJ

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Mixing and fallback models in faint supernova models are supposed to reproduce the abundance patterns of observed carbon-enhanced metal-poor (CEMP) stars in the Galactic halo. A fine tuning of the model parameters for individual stars is required to reproduce the observed ratios of carbon to iron. We focus on extremely metal-poor stars formed out of the ejecta from the mixing and fallback models using a chemical evolution model. Our chemical evolution models take into account the contribution of individual stars to chemical enrichment in host halos together with their evolution in the context of the hierarchical clustering. Parametrized models of mixing and fallback models for Pop. III faint supernovae are implemented in the chemical evolution models with merger trees to reproduce the observed CEMP stars. A variety of choices for model parameters on star formation and metal-pollution by faint supernovae is unable to reproduce the observed stars with [Fe/H] −4 and [C/H] −2, which are the majority of CEMP stars among the lowest metallicity stars. Only possible solution is to form stars from small ejecta mass, which produces an inconsistent metallicity distribution function. We conclude that not all the CEMP stars are explicable by the mixing and fallback models. We also tested the contribution of binary mass transfers from AGB stars that are also supposed to reproduce the abundances of known CEMP stars. This model reasonably reproduces the distribution of carbon and iron abundances simultaneously only if we assume that long-period binaries are favored at [Fe/H] −3.5.

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Section: Introductionmentioning

confidence: 52%

Are Faint Supernovae Responsible for Carbon-enhanced Metal-poor Stars?

Komiya

Suda

Yamada

et al. 2020

ApJ

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“…In spite of the large errors on their four measurements, the indication was clear that the radial velocity of HE 0107−5240 was almost 4 km s −1 larger than it was in the time interval 2001-2006. On this basis, Arentsen et al (2019) suggested that the scenario of mass transfer in this star becomes highly likely. We note that mass transfer can also occur in a very wide binary, if it happens mainly through the stellar wind (Abate et al 2018).…”

Section: Introductionmentioning

confidence: 99%

“…In the meanwhile, Arentsen et al (2019) presented some low quality radial velocity measurements obtained with the High Resolution Spectrograph (Bramall et al 2012) on the Southern African Large Telescope (SALT; Buckley et al 2006). In spite of the large errors on their four measurements, the indication was clear that the radial velocity of HE 0107−5240 was almost 4 km s −1 larger than it was in the time interval 2001-2006.…”

Section: Introductionmentioning

confidence: 99%

ESPRESSO highlights the binary nature of the ultra-metal-poor giant HE 0107−5240

Bonifacio

Molaro

Adibekyan

et al. 2020

A&A

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Context. The vast majority of the known stars of ultra low metallicity ([Fe/H] < −4.5) are known to be enhanced in carbon, and belong to the “low-carbon band” (A(C) = log(C/H)+12 ≤ 7.6). It is generally, although not universally, accepted that this peculiar chemical composition reflects the chemical composition of the gas cloud out of which these stars were formed. The first ultra-metal-poor star discovered, HE 0107−5240, is also enhanced in carbon and belongs to the “low-carbon band”. It has recently been claimed to be a long-period binary, based on radial velocity measurements. It has also been claimed that this binarity may explain its peculiar composition as being due to mass transfer from a former AGB companion. Theoretically, low-mass ratios in binary systems are much more favoured amongst Pop III stars than they are amongst solar-metallicity stars. Any constraint on the mass ratio of a system of such low metallicity would shed light on the star formation mechanisms in this metallicity regime. Aims. We acquired one high precision spectrum with ESPRESSO in order to check the reality of the radial velocity variations. In addition we analysed all the spectra of this star in the ESO archive obtained with UVES to have a set of homogenously measured radial velocities. Methods. The radial velocities were measured using cross correlation against a synthetic spectrum template. Due to the weakness of metallic lines in this star, the signal comes only from the CH molecular lines of the G-band. Results. The measurement obtained in 2018 from an ESPRESSO spectrum demonstrates unambiguously that the radial velocity of HE 0107−5240 has increased from 2001 to 2018. Closer inspection of the measurements based on UVES spectra in the interval 2001–2006 show that there is a 96% probability that the radial velocity correlates with time, hence the radial velocity variations can already be suspected from the UVES spectra alone. Conclusions. We confirm the earlier claims of radial velocity variations in HE 0107−5240. The simplest explanation of such variations is that the star is indeed in a binary system with a long period. The nature of the companion is unconstrained and we consider it is equally probable that it is an unevolved companion or a white dwarf. Continued monitoring of the radial velocities of this star is strongly encouraged.

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“…Caffau et al 2016), but their abundances reflect the chemistry of the gas cloud in which they formed. Recently, Arentsen et al (2019) found four binary systems in a sample of CEMP-no stars, but the fact that some of these stars are binaries is not unexpected.…”

Section: A46 Page 1 Of 10mentioning

confidence: 98%

The CEMP star SDSS J0222–0313: the first evidence of proton ingestion in very low-metallicity AGB stars?

Caffau

Monaco

Bonifacio

et al. 2019

A&A

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Context. Carbon-enhanced metal-poor (CEMP) stars are common objects in the metal-poor regime. The lower the metallicity we look at, the larger the fraction of CEMP stars with respect to metal-poor stars with no enhancement in carbon. The chemical pattern of CEMP stars is diversified, strongly suggesting a different origin of the C enhancement in the different types of CEMP stars. Aims. We selected a CEMP star, SDSS J0222–0313, with a known high carbon abundance and, from a low-resolution analysis, a strong enhancement in neutron-capture elements of the first peak (Sr and Y) and of the second peak (Ba). The peculiarity of this object is a greater overabundance (with respect to iron) of the first s-process peak than the second s-process peak. Methods. We analysed a high-resolution spectrum obtained with the Mike spectrograph at the Clay Magellan 6.5 m telescope in order to derive the detailed chemical composition of this star. Results. We confirmed the chemical pattern we expected; we derived abundances for a total of 18 elements and significant upper limits. Conclusions. We conclude that this star is a carbon-enhanced metal-poor star enriched in elements produced by s-process (CEMP-s), whose enhancement in heavy elements is due to mass transfer from the more evolved companion in its asymptotic giant branch (AGB) phase. The abundances imply that the evolved companion had a low main sequence mass and it suggests that it experienced a proton ingestion episode at the beginning of its AGB phase.

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Binarity among CEMP-no stars: an indication of multiple formation pathways?

Cited by 74 publications

References 100 publications

Are Faint Supernovae Responsible for Carbon-enhanced Metal-poor Stars?

Are Faint Supernovae Responsible for Carbon-enhanced Metal-poor Stars?

ESPRESSO highlights the binary nature of the ultra-metal-poor giant HE 0107−5240

The CEMP star SDSS J0222–0313: the first evidence of proton ingestion in very low-metallicity AGB stars?

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