The <i>s</i> process in AGB stars as constrained by a large sample of barium stars

Cseh, B.; Lugaro, Maria; D’Orazi, V.; Castro, D. B. de; Pereira, C. B.; Plachy, E.; Szabo, Robert M.; Pignatari, M.; Cristallo, S.

doi:10.1051/0004-6361/201834079

Cited by 47 publications

(71 citation statements)

References 115 publications

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“…The rotation induced mixing alters the extend of 13 C pocket (Langer et al 1999), which in turn affects the sprocess abundance pattern. However, a study made by Cseh et al (2018) using the rotating star models available for the metallicity range of Ba stars (Piersanti et al 2013) could not reproduce the observed abundance ratios of stars studied in de Castro et al (2016).…”

Section: Comparison With Fruity Models and A Parametric Model Based Amentioning

confidence: 95%

Characterizing the companion AGBs using surface chemical composition of barium stars

Shejeelammal

Goswami

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Barium stars are one of the important probes to understand the origin and evolution of slow neutron-capture process elements in the Galaxy. These are extrinsic stars, where the observed s-process element abundances are believed to have an origin in the now invisible companions that produced these elements at their asymptotic giant branch (AGB) phase of evolution. We have attempted to understand the s-process nucleosynthesis, as well as the physical properties of the companion stars through a detailed comparison of observed elemental abundances of 10 barium stars with the predictions from AGB nucleosynthesis models, FRUITY. For these stars, we have presented estimates of abundances of several elements, C, N, O, Na, Al, α-elements, Fe-peak elements, and neutron-capture elements Rb, Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu. The abundance estimates are based on high resolution spectral analysis. Observations of Rb in four of these stars have allowed us to put a limit to the mass of the companion AGB stars. Our analysis clearly shows that the former companions responsible for the surface abundance peculiarities of these stars are low-mass AGB stars. Kinematic analysis has shown the stars to be members of Galactic disc population.

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Section: Comparison With Fruity Models and A Parametric Model Based Amentioning

confidence: 95%

Characterizing the companion AGBs using surface chemical composition of barium stars

Shejeelammal

Goswami

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…All models show a clear trend with the yield of heavy s-process elements (Ba, Ce, Nd, Hf, W, Pt, Os) decreasing, relative to the light s-process elements, as the metallicity increases. Shown in panel Ce/Y are the observational data for Ba stars 51,92 in grey. These also indicate a decrease in the Ce/Y ratio as a function of increasing metallicity 51 .…”

Section: Extended Data Fig 5 | Elemental Ratios As a Function Of Metmentioning

confidence: 99%

The origin of s-process isotope heterogeneity in the solar protoplanetary disk

Hunt

Lugaro

et al. 2019

Nat Astron

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Rocky asteroids and planets display nucleosynthetic isotope variations that are attributed to the heterogeneous distribution of stardust from different stellar sources in the solar protoplanetary disk. Here we report new high precision palladium isotope data for six iron meteorite groups, which display smaller nucleosynthetic isotope variations than the more refractory neighbouring elements. Based on this observation we present a new model in which thermal destruction of interstellar medium dust results in an enrichment of s-process dominated stardust in regions closer to the Sun. We propose that stardust is depleted in volatile elements due to incomplete condensation of these elements into dust around asymptotic giant branch (AGB) stars. This led to the smaller nucleosynthetic variations for Pd reported here and the lack of such variations for more volatile elements. The smaller magnitude variations measured in heavier refractory elements suggest that material from high-metallicity AGB stars dominated stardust in the Solar System. These stars produce less heavy s-process elements (Z ≥ 56) compared to the bulk Solar System composition.The protoplanetary disk from which our Solar System formed incorporated dust that was inherited from the collapsing molecular cloud. A few per cent of this dust formed around stars with active nucleosynthesis and retained the extreme isotopic fingerprint of its formation environment 1,2 . This dust, which is isotopically anomalous compared to Solar System compositions, is here termed stardust. However, it is often also referred to as presolar grains when found in meteorites. Most stardust in primitive meteorites originates from asymptotic giant branch (AGB) stars, the site of s-process nucleosynthesis, with only small contributions from supernovae environments 3 . The majority of the dust in the solar protoplanetary disk grew in the interstellar medium (ISM) from a well-mixed gas phase as mantles on pre-existing nuclei. These mantles likely inherited the composition of the local ISM, i.e., a near solar isotopic composition 1 .Nucleosynthetic isotope variations, relative to Earth, are well established for a range of elements in bulk meteorites 4 . These variations mostly reflect the heterogeneous distribution of isotopically distinct dust in the protoplanetary disk. It is generally thought that this heterogeneity was established, at least in part, due to processes occurring in the protoplanetary disk itself. Physical sorting of grains, either by mineralogical type 5 or size 6 , and selective destruction of stardust by thermal processing in the protoplanetary disk 7-9 or by aqueous alteration on parent bodies 10 , have all been proposed as possible mechanisms to generate isotope heterogeneity. While these individual processes can explain nucleosynthetic variations for specific elements, it is debated whether a unifying explanation for all elemental trends exists 11 . Therefore, considerable uncertainty remains as to which processes were important for dust processing in the protoplanet...

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“…In Fig. 4, we also show theoretical s-process predictions from two groups: the FRUITY 1 yields from Cristallo et al (2015), which cover a range in metallicity from [Fe/H] ≈ 0.1 to −2.3, and the 1 http://fruity.oa-teramo.inaf.it/ Monash yields (Fishlock et al 2014;Karakas & Lugaro 2016), which cover a range in metallicity from [Fe/H] = +0.3 to −1.2 (similarly to Cseh et al 2018). For both sets of models, we show results from initial masses between 1.5 and 3 M .…”

Section: Comparison To Agb Yieldsmentioning

confidence: 81%

Discovery of s-process enhanced stars in the LAMOST survey

Norfolk

Casey

Karakas

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Here we present the discovery of 895 s-process-rich candidates from 454 180 giant stars observed by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) using a data-driven approach. This sample constitutes the largest number of s-process enhanced stars ever discovered. Our sample includes 187 s-process-rich candidates that are enhanced in both barium and strontium, 49 stars with significant barium enhancement only and 659 stars that show only a strontium enhancement. Most of the stars in our sample are in the range of effective temperature and log g typical of red giant branch (RGB) populations, which is consistent with our observational selection bias towards finding RGB stars. We estimate that only a small fraction (∼0.5 per cent) of binary configurations are favourable for s-process enriched stars. The majority of our s-process-rich candidates (95 per cent) show strong carbon enhancements, whereas only five candidates (<3 per cent) show evidence of sodium enhancement. Our kinematic analysis reveals that 97 per cent of our sample are disc stars, with the other 3 per cent showing velocities consistent with the Galactic halo. The scaleheight of the disc is estimated to be $z_{\rm h}=0.634 \pm {0.063}\, \mathrm{kpc}$, comparable with values in the literature. A comparison with yields from asymptotic giant branch (AGB) models suggests that the main neutron source responsible for the Ba and Sr enhancements is the 13C(α,n)16O reaction. We conclude that s-process-rich candidates may have received their overabundances via mass transfer from a previous AGB companion with an initial mass in the range $1\!-\!3\, \mathrm{M}_{\odot }$.

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The s process in AGB stars as constrained by a large sample of barium stars

Cited by 47 publications

References 115 publications

Characterizing the companion AGBs using surface chemical composition of barium stars

Characterizing the companion AGBs using surface chemical composition of barium stars

The origin of s-process isotope heterogeneity in the solar protoplanetary disk

Discovery of s-process enhanced stars in the LAMOST survey

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