Are some CEMP-<i>s </i>stars the daughters of spinstars?

Choplin, Arthur; Hirschi, Raphaël; Meynet, Georges; Ekström, Sylvia

doi:10.1051/0004-6361/201731948

Cited by 49 publications

(45 citation statements)

References 47 publications

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“…5 we show [Sr/Ba] vs. relative C and O abundances compared to generalised FRMS yields (Frischknecht et al 2012) with an average of [Sr/Ba] ∼ 0.5 and AGB yields ([Sr/Ba] ∼ −0.5 from predictions of metal-poor AGB stars with 1.5-2 M ; Cristallo et al 2011). The bottom panel of the same figure shows the separation of FRMS using O predictions from Choplin et al (2017), contrasting with the above described AGB yields. Despite some of the stars falling slightly off the predictions, there is an overall good agreement between the results illustrated by the two panels.…”

Section: Abundance Resultsmentioning

confidence: 98%

“…The Sr/Ba ratio is different in AGB stars and FRMS, which makes Sr/Ba an efficient and useful descriptor to trace possible formation sources, in the sense that only two elements/absorption features need to be analysed to derive this abundance ratio. Additionally, Choplin et al (2017) showed that the Sr/Ba ratio, together with the O production in FRMS, is much higher than in AGB stars.…”

Section: Abundance Resultsmentioning

confidence: 99%

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Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo

Hansen

Koch

et al. 2019

A&A

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Carbon-enhanced metal-poor (CEMP) stars span a wide range of stellar populations, from bona fide second-generation stars to laterforming stars that provide excellent probes of binary mass transfer and stellar evolution. Here we analyse 11 metal-poor stars (8 of which are new to the literature), and demonstrate that 10 are CEMP stars. Based on high signal-to-noise (SNR) X-Shooter spectra, we derive abundances of 20 elements (CEu). From the high SNR spectra, we could trace the chemical contribution of the rare earth elements (REE) from various possible production sites, finding a preference for metal-poor low-mass asymptotic giant branch (AGB) stars of 1.5 M in CEMP-s stars, while CEMP-r/s stars may indicate a more massive AGB contribution (2-5 M ). A contribution from the r-process -possibly from neutron star -neutron star mergers (NSM), is also detectable in the REE stellar abundances, especially in the CEMP-r/s sub-group rich in both slow and rapid neutron-capture elements. Combining spectroscopic data with Gaia DR2 astrometric data provides a powerful chemodynamical tool for placing CEMP stars in the various Galactic components, and classifying CEMP stars into the four major elemental-abundance sub-groups, dictated by their neutron-capture element content. The derived orbital parameters indicate that all but one star in our sample (and the majority of the selected literature stars) belong to the Galactic halo. They exhibit a median orbital eccentricity of 0.7, and are found on both prograde and retrograde orbits. We find that the orbital parameters of CEMP-no and CEMP-s stars are remarkably similar in the 98 stars we study. A special case is the CEMP-no star (HE 0020-1741), with very low Sr and Ba content, which possesses the most eccentric orbit among the stars in our sample, passing close to the Galactic centre. Finally, we propose an improved scheme to sub-classify the CEMP stars, making use of the Sr/Ba ratio, which can also be used to separate very metal-poor stars from CEMP stars. We explore the use of [Sr/Ba] vs. [Ba/Fe] in 93 stars in the metallicity range −4.2 [Fe/H]< −2. We show that the Sr/Ba ratio can also be successfully used for distinguishing CEMP-s, CEMP-r/s and CEMP-no stars. The Sr/Ba ratio is also a powerful astro-nuclear indicator, since the metal-poor AGB stars exhibit very different Sr/Ba ratios, compared to fast rotating massive stars and NSM, and it is reasonably unbiased by NLTE and 3D corrections.

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Section: Abundance Resultsmentioning

confidence: 98%

Section: Abundance Resultsmentioning

confidence: 99%

Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo

Hansen

Koch

et al. 2019

A&A

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“…We note that in Figure 8 the single CEMP-s stars seem to be preferentially located on the lower side of the A(C) distribution of the CEMP-s stars. Choplin et al (2017) model the abundances of the single CEMP-s stars with massive spinstar models, and succeed for three out of the four modelled stars. Spinstar models are also employed to explain the abundances of CEMP-no stars (e.g.…”

Section: A High Fraction Of Binaries Among Intermediate/high Carbon Bmentioning

confidence: 94%

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

Arentsen

Starkenburg

Shetrone

et al. 2019

A&A

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Carbon-enhanced metal-poor (CEMP) stars comprise a large percentage of stars at the lowest metallicities. The stars in the CEMP-no subcategory do not show any s-process enhancement and therefore cannot easily be explained by transfer of carbon and s-process elements from a binary AGB companion. We have performed radial velocity monitoring of a sample of 22 CEMP-no stars to further study the role binarity plays in this type of CEMP star. We find four new binary CEMP-no stars based on their radial velocity variations, thereby significantly enlarging the population of known binaries to a total of eleven. One of the new binary systems is HE 0107−5240, one of the most iron-poor stars known, supporting the binary transfer model for the origin of the abundance pattern of this star. In our sample we find a difference in binary fraction depending on the absolute carbon abundance, with a binary fraction of 47 +15 −14 % for stars with higher absolute carbon abundance and 18 +14 −9 % for stars with lower absolute carbon abundance. This potentially implies a relation between a high carbon abundance and the binarity of a metal-poor star. Although binarity does not equate to mass transfer, there is a possibility that a CEMP-no star in a binary system has been polluted and care has to be taken in the interpretation of their abundance patterns. We furthermore demonstrate the potential of Gaia to discover additional binary candidates.

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“…Photometric and spectroscopic bservations of the electromagnetic counterpart (AT 2017gfo;Cowperthwaite et al 2017;Drout et al 2017;Kilpatrick et al 2017;Shappee et al 2017) of the recent LIGO/VIRGO detection of a binary neutron star merger in 2017 (GW170817; Abbott et al 2017a,b) provided direct evidence of main r-process element production. An additional source, operation of an s-process in spinstars, has been recently suggested (Frischknecht et al 2012;Cescutti et al 2013;Frischknecht et al 2016;Choplin et al 2017Choplin et al , 2018, which could also possibly produce Ba. Following these, the dominant site for Ba (along with carbon) production transitions to low-to intermediatemass thermally pulsating AGB stars, where the main s-process operates.…”

Section: The Origin and Evolution Of Carbon Iron And Bariummentioning

confidence: 99%

Origin of the CEMP-no Group Morphology in the Milky Way

Yoon

Tian

Whitten

2019

ApJ

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The elemental-abundance signatures of the very first stars are imprinted on the atmospheres of CEMP-no stars, as various evidence suggests they are bona-fide second-generation stars. It has recently been recognized that the CEMP-no stars can be sub-divided into at least two groups, based on their distinct morphology in the A(C)-[Fe/H] space, indicating the likely existence of multiple pathways for their formation. In this work, we compare the halo CEMP-no group morphology with that of stars found in satellite dwarf galaxies of the Milky Way -a very similar A(C)-[Fe/H] pattern is found, providing clear evidence that halo CEMP-no stars were indeed accreted from their host mini-halos, similar in nature to those that formed in presently observed ultra faint dwarfs (UFDs) and dwarf spheroidal (dSph) galaxies. We also infer that the previously noted "anomalous" CEMP-no halo stars (with high A(C) and low [Ba/Fe] ratios) that otherwise would be associated with Group I may have the same origin as the Group III CEMP-no halo stars, by analogy with the location of several Group III CEMP-no stars in the UFDs and dSphs and their distinct separation from that of the CEMP-s stars in the A(Ba)-A(C) space. Interestingly, CEMP-no stars associated with UFDs include both Group II and Group III stars, while the more massive dSphs appear to have only Group II stars. We conclude that understanding the origin of the CEMP-no halo stars requires knowledge of the masses of their parent mini-halos, which is related to the amount of carbon dilution prior to star formation, in addition to the nature of their nucleosynthetic origin.

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Are some CEMP-s stars the daughters of spinstars?

Cited by 49 publications

References 47 publications

Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo

Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo

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

Origin of the CEMP-no Group Morphology in the Milky Way

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