To Ba or not to Ba: Enrichment in<i>s</i>-process elements in binary systems with WD companions of various masses

Merle, Thibault; Jorissen, A.; Eck, S. Van; Masseron, T.; Winckel, H. Van

doi:10.1051/0004-6361/201526944

Cited by 32 publications

(52 citation statements)

References 59 publications

(97 reference statements)

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“…Table B.1. List of measured lines: wavelength λ, excitation potential χ exc , adopted oscillator strengths log g f , and source: (a) Merle et al (2016), (b) GES line list v5 (Heiter et al 2015), (c) adjusted to reproduce solar and/or Arcturus abundances, and (d) VALD. The effective log g f is given for lines whose hyperfine structure was taken into account (identified with an asterisk after the wavelength).…”

Section: Discussionmentioning

confidence: 99%

“…7, moreover, we see that there is a small excess of systems with mass ratios between 0.1 and 0.2; these systems would correspond to lower mass WDs, that is those below 0.46 M , namely, He WDs. Such WDs cannot have been the core of a thermally pulsing AGB star where the s-process material needed to pollute the barium star has been synthesised (Merle et al 2016). Therefore, this cannot be the correct explanation for the presence of that peak.…”

Section: Mass-ratio Distributionmentioning

confidence: 99%

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The mass-ratio and eccentricity distributions of barium and S stars, and red giants in open clusters

Swaelmen

Boffin

Jorissen

et al. 2017

A&A

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Context. A complete set of orbital parameters for barium stars, including the longest orbits, has recently been obtained thanks to a radial-velocity monitoring with the HERMES spectrograph installed on the Flemish Mercator telescope. Barium stars are supposed to belong to post-mass-transfer systems. Aims. In order to identify diagnostics distinguishing between pre-and post-mass-transfer systems, the properties of barium stars (more precisely their mass-function distribution and their period -eccentricity (P − e) diagram) are compared to those of binary red giants in open clusters. As a side product, we aim to identify possible post-mass-transfer systems among the cluster giants from the presence of s-process overabundances. We investigate the relation between the s-process enrichment, the location in the (P − e) diagram, and the cluster metallicity and turn-off mass. Methods. To invert the mass-function distribution and derive the mass-ratio distribution, we used the method pioneered by Boffin et al. (1992) that relies on a Richardson-Lucy deconvolution algorithm. The derivation of s-process abundances in the open-cluster giants was performed through spectral synthesis with MARCS model atmospheres. Results. A fraction of 22% of post-mass-transfer systems is found among the cluster binary giants (with companion masses between 0.58 and 0.87 M , typical for white dwarfs), and these systems occupy a wider area than barium stars in the (P − e) diagram. Barium stars have on average lower eccentricities at a given orbital period. When the sample of binary giant stars in clusters is restricted to the subsample of systems occupying the same locus as the barium stars in the (P − e) diagram, and with a mass function compatible with a WD companion, 33% (=4/12) show a chemical signature of mass transfer in the form of s-process overabundances (from rather moderate -about 0.3 dex -to more extreme -about 1 dex). The only strong barium star in our sample is found in the cluster with the lowest metallicity in the sample (i.e. star 173 in NGC 2420, with [Fe/H] = −0.26), whereas the barium stars with mild s-process abundance anomalies (from 0.25 to ∼ 0.6 dex) are found in the clusters with slightly subsolar metallicities. Our finding confirms the classical prediction that the s-process nucleosynthesis is more efficient at low metallicities, since the s-process overabundance is not clearly correlated with the cluster turn-off (TO) mass; such a correlation would instead hint at the importance of the dilution factor. We also find a mild barium star in NGC 2335, a cluster with a large TO mass of 4.3 M , which implies that asymptotic giant branch stars that massive still operate the s-process and the third dredge-up.

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Section: Discussionmentioning

confidence: 99%

Section: Mass-ratio Distributionmentioning

confidence: 99%

The mass-ratio and eccentricity distributions of barium and S stars, and red giants in open clusters

Swaelmen

Boffin

Jorissen

et al. 2017

A&A

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“…Recent observations have shown that the CEMP stars are truly equivalent to CH and barium stars (Starkenburg et al, 2014), and that the amount of accreted material is a function of orbital period (Merle et al, 2016). The properties of these systems allow direct tests of uncertain physical processes such as wind accretion efficiency, wind Roche-lobe overflow (Abate et al, 2013), mixing in the accreting star (e.g.…”

Section: Wind-polluted Stars and Ancient Nucleosynthesismentioning

confidence: 99%

Dawes Review 6: The Impact of Companions on Stellar Evolution

Marco

Izzard

2017

Publ. Astron. Soc. Aust.

185

136

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Astrophysicists are increasingly taking into account the effects of orbiting companions on stellar evolution. New discoveries have underlined the role of binary star interactions in a range of astrophysical events, including some that were previously interpreted as being due uniquely to single stellar evolution. We review classical binary phenomena, such as type Ia supernovae, and discuss new phenomena, such as intermediate luminosity transients, gravitational wave-producing double black holes, and the interaction between stars and their planets. Finally, we reassess well-known phenomena, such as luminous blue variables, in light of interpretations that include both single and binary stars. At the same time we contextualise the new discoveries within the framework of binary stellar evolution. The last decade has seen a revival in stellar astrophysics as the complexity of stellar observations is increasingly interpreted with an interplay of single and binary scenarios. The next decade, with the advent of massive projects such as the Square Kilometre Array, the James Webb Space Telescope, and increasingly sophisticated computational methods, will see the birth of an expanded framework of stellar evolution that will have repercussions in many other areas of astrophysics such as galactic evolution and nucleosynthesis.

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“…Accordingly, the ability to detect binary (and exoplanet) orbital motions of even very low-amplitude and long-period binaries has not only improved owing to reduced observational errors, but it is also becoming increasingly limited by intrinsic variability in the target star itself. Moreover, not all potential binary companions are able to evolve past the AGB stage and transfer s-process enriched material to the surviving star, so only binary systems with companions of present-day mass in the white dwarf range of 0.5-1.4 M (Merle et al 2016) need concern us here. We therefore discuss the binary status of our potentially single stars separately in the following section.…”

Section: Identifying the Single And Binary Starsmentioning

confidence: 99%

The role of binaries in the enrichment of the early Galactic halo

Hansen

Andersen

Nordström

et al. 2016

A&A

139

146

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Context. Detailed spectroscopic studies of metal-poor halo stars have highlighted the important role of carbon-enhanced metal-poor (CEMP) stars in understanding the early production and ejection of carbon in the Galaxy and in identifying the progenitors of the CEMP stars among the first stars formed after the Big Bang. Recent work has also classified the CEMP stars by absolute carbon abundance, A(C), into high-and low-C bands, mostly populated by binary and single stars, respectively. Aims. Our aim is to determine the frequency and orbital parameters of binary systems among the CEMP-s stars, which exhibit strong enhancements of neutron-capture elements associated with the s-process. This allows us to test whether local mass transfer from a binary companion is necessary and sufficient to explain their dramatic carbon excesses. Methods. We have systematically monitored the radial velocities of a sample of 22 CEMP-s stars for several years with ∼monthly, high-resolution, low S/N échelle spectra obtained at the Nordic Optical Telescope (NOT) at La Palma, Spain. From these spectra, radial velocities with an accuracy of ≈100 m s −1 were determined by cross-correlation with optimised templates. Results. Eighteen of the 22 stars exhibit clear orbital motion, yielding a binary frequency of 82 ± 10%, while four stars appear to be single (18 ± 10%). We thus confirm that the binary frequency of CEMP-s stars is much higher than for normal metal-poor giants, but not 100% as previously claimed. Secure orbits are determined for eleven of the binaries and provisional orbits for six long-period systems (P > 3000 days), and orbital circularisation timescales are discussed. Conclusions. The conventional scenario of local mass transfer from a former asymptotic giant branch (AGB) binary companion does appear to account for the chemical composition of most CEMP-s stars. However, the excess of C and s-process elements in some single CEMP-s stars was apparently transferred to their natal clouds by an external (distant) source. This finding has important implications for our understanding of carbon enrichment in the early Galactic halo and some high-redshift damped lyman alpha (DLA) systems, and of the mass loss from extremely metal-poor AGB stars.

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To Ba or not to Ba: Enrichment ins-process elements in binary systems with WD companions of various masses

Cited by 32 publications

References 59 publications

The mass-ratio and eccentricity distributions of barium and S stars, and red giants in open clusters

The mass-ratio and eccentricity distributions of barium and S stars, and red giants in open clusters

Dawes Review 6: The Impact of Companions on Stellar Evolution

The role of binaries in the enrichment of the early Galactic halo

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